To survey the etiology of adverse prenatal outcome in overweight. This comparative cohort study was conducted from 2010 to 2012. Total 440 gravid women 220were overweight and 220 normal weight pregnant women during at the first visit of pregnancy and third trimester were assessed. The risks for preterm labor, gestational hypertension, pre-eclampsia, gestational diabetes, caesarian section and Macrosomia were higher for those who were overweight at the third trimester of pregnancy (P < 0.05). Maternal BMI was associated with a higher risk for gestational hypertension, gestational diabetes, preterm labor, preeclampsia, caesarian section and fetal macrosomia (P< 0.05). This research demonstrates that maternal BMI was associated with increased risks for adverse pregnancy outcomes.