Introduction: Iran has experienced a dramatic fertility decline in recent decades. The Total Fertility Rate (TFR) reached the below-replacement level in 2000 and further declined to 1.8 in 2011 before rising to around 2.1 by 2016 and then falling to 1.8 by 2019. Tehran city has been a vanguard of low fertility as the TFR has been around 1.5 children per woman in recent years. As fertility falls to a low level, the second and higher birth intervals increase which could have significant impacts on the level of fertility. Various theories and hypotheses have explained low fertility. Recently, however, gender equity has emerged as a key link in explaining the phenomenon of low fertility (Cook 2003; McDonald 2000). Based on gender equity theory, many women, especially those with higher education and career prospects, may see their role as mothers and wives in conflict with other roles under the influence of new egalitarian ideas they have acquired in person-centered institutions. Therefore, they try to limit their fertility because fertility takes a lot of time and energy from them. Thus, low fertility rates will continue unless gender equity in family-centered institutions increases much faster than in the past. In the context of high gender equity in individual-centered institutions, higher gender equity in family-oriented social institutions will lead to increased fertility. Failure to change gender roles in family life, while women want to take advantage of more economic and educational opportunities, leads to reduced fertility (McDonald 2000). Three aspects of gender equity in the family, including the spouse's participation in household chores, women's attitudes toward gender roles, as well as the spouse's support and participation in the affairs of children, are valuable in explaining fertility decline (Bianchi, et al. 2000; Mills, et al. 2008). Recent studies in low-fertility settings have attributed long birth intervals and low fertility to gender role attitudes and role division within the family (Fukuda 2017; Miettinen et al 2011). This study aims to investigate the effect of the gender division of labor and attitudes on the second birth interval in Tehran city. Materials and Methods:This study used a sub-sample of data from the ‘Iran Fertility Transition Survey’ conducted in five provinces of Iran (including Tehran) in 2017. The sample comprised 363 married women aged 15-49 years old and had at least one child in Tehran city. The Kaplan-Meier test was used to determine the second birth interval. To investigate its relationship with attitude and gender division of labor, survival models including Cox proportional, exponential, Weibel, Gompertz, Log Normal Logl Logistic, and Gamma Generalized models were fitted. In order to consider the dependence on survival times, a common fragility model with gamma distribution was tested. Based on the Akaik criterion, the generalized gamma model was selected as the most appropriate model. Discussion of Results and Conclusions: The results showed that the median time of first birth to second birth among the sample was 84 months. Based on cumulative survival ratios within 120 months (10 years) of the time of first birth, 70% of women had a second child, meaning that 30% of them were likely to remain single-child. According to the results, one-third of women indicated that their husbands were involved in taking care of their children. Regarding the division of household affairs, 86% of women did the housework (cleaning, cooking, etc.) alone and only 14% did it with the participation of their husbands. In addition, about half of the women had egalitarian gender attitudes, and less than a third had traditional gender attitudes.According to Kaplan Meyer's estimates, the median interval between the first and second birth among women who do the housework alone and take care of the children alone is 6 and 2 months longer, respectively, than the women whose husbands participate in such matters. The analyses revealed also a significant relationship between gender attitudes and second birth interval. Women with an egalitarian attitude delayed their second birth by about 30 months more than other women. The results of multivariate analysis with the generalized gamma model also showed that having a modern gender attitude increases the second birth interval.Participation of men in domestic work had no significant effect on the second birth interval. Despite the transition of the society from traditional to modern in many respects, due to the dominance of patriarchal structures and low gender equity in the family, the division of household chores based on gender remains, and women are mainly responsible for housework. Even after controlling for employment situation, there was no significant relationship between the division of labor in the home and the interval between the first and second birth. This finding may have been influenced by the small sample size in the participatory category, given that the majority of women do housework alone, and thus, the statistical analysis did not show a significant difference between the independent variables and the second birth timing. However, after controlling for contextual variables and socio-economic characteristics, the results showed that gender division of labor in child affair had a significant effect on the second birth interval, and the lower participation of men in child affairs increased the second birth interval.The results also revealed that such variables as education, the ideal number of children at the time of marriage, and the interval between marriage to first birth had a significant effect on the second birth interval. Having a diploma degree and lower as compared to those with higher levels of education has reduced the second birth interval. The ideal number of children at the time of marriage also had a decreasing effect, as those with a higher ideal number of children at the time of marriage had a lower second birth interval. Furthermore, those with a longer interval between marriage and the first birth experienced a longer second birth interval. Finally, there was a significant difference between the second birth interval by marriage cohort. Those who married in the 1980s experienced a shorter birth interval as compared to the 2000s marriage cohort.According to McDonald (2000) and Goldshider (2000), the conflict between behavior and attitudes in the family and society can be the source of change in family decisions, the formation of low fertility intentions and behaviors, including delay in fertility and increasing the interval between births leading to smaller family norm and size. The findings of this article are in line with the theory of gender equity as having egalitarian gender attitudes and unequal division of care of children has led to a delay in the second birth. In other words, having egalitarian gender attitudes among women only leads to increased fertility when males also participate in decision making as well as household and children affairs. Giving or taking responsibility for housework by women is rooted in a gender ideology that is different or even conflicting with the gender ideology of women today. Therefore, such a difference in attitude and behavior can lead to a longer interval between births and low fertility behaviors and intentions in Tehran city. In order to implement policies to increase fertility, in addition to striving for a sustainable economy and providing an optimistic outlook for the future, family-friendly policies must embrace a broad framework of cultural values that support men's participation in domestic affairs and reduce gender inequality, thereby preventing further delay on the second birth interval leading to fertility increase.