Background. For most women in the postpartum period, six to 52 weeks after childbirth, participation in physical activity is limited. New mothers often report inability to exercise, due in part to feeling isolated and exhausted. The literature offers contradictory arguments regarding the influence of exercise on Postnatal Depression (PND). Therefore, this study aimed to: (1) determine the variables associated with physical activity during the postpartum period; (2) investigate the relationship between physical activity and PND; and (3) explore the enablers and barriers to physical activity in a sample of postpartum women.Method. This multi-method study employed a cross-sectional correlational design in Stage One and a qualitative design in Stage Two. In Stage One 150 postpartum women recruited from the Western Australian metropolitan Child Health Clinics were sent a questionnaire. In Stage Two 14 postpartum women who participated in the survey were also interviewed. Survey data were analysed using SPSS to conduct multiple regression analysis and the interviews were thematically coded.Results. The study did not demonstrate an association between physical activity participation (PAP) and PND. However, psychosocial factors, parental confidence, partner support and social support were significantly associated with PND. The predictors of the mother’s PAP were the age of her baby, her education level, number of children, family income, parental confidence, partner support and lack of time. Lack of information, lack of confidence, lack of knowledge and poor access to public transport were the barriers to the living domain of PAP. Lack of money was associated with reduced exercise. Results from Stage Two supported the findings from Stage One and illustrated that mothers were more likely to participate in physical activity if they had greater social support, particularly partner support, and if they were confident in their parenting ability.Conclusion. The study was unable t