Abstract: Objective To determine the influence of pre-pregnant body mass index(BMI) and weight gain during pregnancy on the occurrence of pregnancy-induced hypertension(PIH) and birth weight. Methods Pre-pregnant BMI and pregnancy weight gain of 769 mothers giving full-term birth to a single baby for the first time were measured and the pregnancy outcomes were followed up. Results(1) The incidence of PIH and fetal macrosomia was significantly higher in the overweight group than in the normal weight and underweight groups(P<0.01 and P<0.05, respectively), but differed little between the latter two groups(P>0.05). Underweight mothers were more likely to give birth to babies with low birth weight than the normal and overweight mothers(P<0.01), but the likelihood was similar between the latter two groups(P>0.05).(2) Irrespective of the pre-pregnant BMI, PIH and fetal macrosomia occurred at higher rates with the mothers with pregnancy weight gain no less than 18 kg(P<0.01), whereas low birth weight was significantly more likely with mothers with pregnancy weight gain less than 9 kg(P<0.01).(3) A weight gain during pregnancy over 18 kg gave rise to higher risk of PIH in normal and underweight mothers, but in overweight group, PIH occurred at a significantly higher rates when a weight gain more than 9 kg was recorded(P<0.05). The incidence of fetal macrosomia was significantly higher when the maternal weight gain exceeded 18 kg in the normal weight group(P<0.01), and low birth weight occurred more frequently in relation to a maternal weight gain less than 9 kg in the normal and underweight groups(P<0.01). Conclusion Pre-pregnant BMI and weight gain during pregnancy can be important factors influencing the occurrence of PIH and the neonates’ birth weight.