ObjectiveInvestigate factors associated with symptoms of postpartum depression in mothers from families in social vulnerability. MethodsInformation was used from the baseline of a randomized trial to assess a child development program that enrolled 3,242 children < 12 months of age from beneficiary families of the Bolsa Família Program residing in 30 municipalities (counties) in six states of Brazil. The Edinburgh Postnatal Depression Scale (EPDS) was applied to the mothers, and depression was defined as score ≥10. Information on the mother (schooling, age, parity, marital status, skin color, smoking, number of prenatal appointments, and planning of the pregnancy), family (paternal schooling, household crowding, support from the child's father and the family during the pregnancy, and number of children under 7 years living in the household), and infant (sex, gestational age, birthweight, Apgar score, and child's age at the time of the interview) was collected. Prevalence rates for depressive symptoms were calculated with crude and adjusted odds ratios (OR) and 95% confidence intervals (95%CI), using hierarchical logistic regression, in a multilevel model. ResultsThe analysis included 3,174 mothers with information on EPDS. The interviews were conducted on average 7.9 months (standard deviation= 2.9) after childbirth. Overall prevalence of depressive symptoms was 26.5% (25.0-28.1%). In the adjusted analysis, higher parity was associated with higher odds of postpartum depression (p <0.001). Women with ≥3 previous deliveries showed an odds 84% higher of presenting depressive symptoms (OR= 1.84; 1.43-2.35) than primiparae. Higher maternal and paternal schooling, presence of husband or partner, and having received support from the child's father and the family during the pregnancy were protective factors against postpartum depression. ConclusionThe study showed high prevalence of postpartum depressive symptoms. Promotion of parental education, alongside with the promotion of support to the woman during pregnancy by the child's father and by the family, as well as family planning leading to birth spacing are measures that may help to prevent postpartum depressive symptoms.