Postpartum depression increases the rate of complications for mother and infant. Few studies on postpartum depression have been undertaken on pregnant women with a low socioeconomic status. The present study aims to recognize the prevalence of postpartum depression and association with risk factors in low socioeconomic populations. Predicting risk factors during pregnancy for postpartum depression are so important. 451 low income pregnant women referred to health care centres, participated in a prospective study. Questionnaires covered demographics and, obstetrics and psychological characteristics were collected by interviews. Edinburgh Postnatal Depression Scale (EPDS) was used to define depression in pregnancy as a sum score ≥ 10 and in postpartum as a sum score ≥ 13 at gestational week 28. The mean participant age was 25 years. Most of them had moderate perceived stress (61%), low self-esteem (63.2%), low perceived social support (67.6%), and low quality of marital relationship (43.5%). Fear related to childbirth was high in more than half of respondents (50.8%) and 58.9% had prenatal depression. The frequency of postnatal depression was 39% in participants. Those with postpartum depression had lower self-esteem scores, higher perceived stress and higher childbirth related fear in both mothers with postpartum depression and mothers without it. The prevalence of depression in pregnancy was higher in low socio-economic primigravidea from Iran. The increased risk persisted after adjustment for risk factors.