Abstract: Objective To understand the prevalence rate of prenatal depression, and the influence of depression during each pregnancy trimester on gestational body weight gain. Methods Pregnant women who received prenatal care in a women and children's hospital in Zhejiang province were recruited in our study. Well self-constructed questionnaire was used to collect information about their demographics, reproductive history, health status and life behaviors at 8-12th, 22-26thgestational weeks and after 32thgestational week. Self-Rating Depression Scale (SDS) were used to assess degree of depression. Results The incidence of depression during 1st, 2nd and 3rd trimesters were 48.8%, 35.0% and 34.9%respectively. And all SDS scores in three trimesters were higher than those of Chinese norm.SDS scores in 1st trimester were negatively related with BMI (=-0.01, P=0.0184). No association between prenatal depression and gestational body weight gain was observed. Conclusion he prevalence rate of depression during pregnancy was high. Gestational mental health interventions should be taken to improve maternal and fetal health.