Having a late chronotype, that is, the tendency to go to sleep and wake up at later hours, influences an individual's physical and mental health. Despite a few studies noting the association of chronotype with healthy dietary patterns, this relationship remains unclear.This study aimed to describe the association of chronotype with healthful and unhealthful plant-based diet quality in female Japanese undergraduate students.Cross-sectional.A total of 218 female university students in Tokyo, Japan.Healthful and unhealthful plant-based dietary index-Japanese version (hPDI-J and uPDI-J), calculated using the validated brief-type self-administered diet history questionnaire.A five-model stepwise multiple linear regression analysis was conducted. Independent variables were hPDI-J and uPDI-J scores, and dependent variables were various lifestyle habits related to the circadian rhythm and demographic characteristics.Mean (standard deviation) sleep duration, midpoint of sleep, sleep latency time, and social jetlag were 411 (60) min, 03:56 (00:57), 21 (27) min, and 50 (39) min, respectively. Chronotype and several variables, such as residential status, energy and alcohol intake, and nutritional knowledge, were associated with healthful and unhealthful plant-based diet quality. Individuals who had higher hPDI-J scores were more likely to have an earlier chronotype (β = -0.168, P = 0.019) and better nutritional knowledge (β = 0.164, P = 0.022) than those with lower hPDI-J scores. Individuals were more likely to have higher uPDI-J scores if they were living alone (β = -0.301, P 0.001), had a later chronotype (β = 0.181, P = 0.001), higher frequency of snacking (β = 0.164, P = 0.019), lower total energy (β = -0.445, P 0.001), and worse nutritional knowledge (β = -0.172, P = 0.001).This study provided new evidence as to the relationship between sleep and dietary habits, the interaction of which may affect women's health.