Psychosocial risk conditions can predict postpartum depression (PPD) which can reduce maternal investment into child. We examined, in high-risk Brazilian mothers, PPD predictors measured during pregnancy, and PPD effects on maternal behaviors measured at 4-5 months. 35 depressed (D) and 38 nondepressed (ND) mothers had four behaviors (gaze, smile, vocalization and touch) and three interaction styles (intrusive, withdrawn and good interaction) coded. At 4 months, 48% of mothers presented PPD. Lower levels of education, shorter pregnancy, higher marital conflict and greater prior history of depression were found as PPD predictors. D and ND mothers equally gazed, smiled and touched, while only D mothers vocalized less to their children. Thus, lower levels of education, shorter pregnancy, higher marital conflict and greater prior history of depression catalyzed PPD emergence. PPD reduced maternal investment through lower vocalization during early mother-infant interaction. Finally, both D and ND mothers mostly behaved as good interaction partners.