Postpartum depression (PPD) is the most common psychiatric complication observed in women after they give birth. Some women are particularly sensitive to hormonal changes, starting in early menarche, thus increasing their vulnerability to psychological stressing agents that are triggered by environmental and physiological factors throughout their lives. Decreased serum brain-derived neurotrophic factor (BDNF) levels have been associated to different neuropsychiatric conditions and BDNF has been considered as a candidate marker for such dysfunctions. The goal of this study was to compare the levels of BDNF between mothers who suffer from PPD and healthy control mothers as well as to searching for associations between BDNF levels and the severity of PPD. This is a case-control study including 36 mothers with PPD and 36 healthy control mothers. PPD was defined according to the Beck Depression Inventory (BDI). Serum BDNF was assayed with the sandwich ELISA method. Results: Serum levels of BDNF were significantly lower in women with PPD than in control mothers (P ≤ 0.03). A significant negative correlation between BDI score and serum BDNF levels was observed (P ≤ 0.02 and r = -0.29). Our study demonstrated that low BDNF levels are associated with PPD. This result point out to the potential usage of BDNF in the screening of PPD, which could promote early treatment and, therefore, reduce the burden to the PPD women and to the health system.