BACKGROUND: This prospective study was performed to evaluate factors influencing weight changes pregnancy period and pospartum period. METHODS: A total of 195 women followed by prenatal care of the department of OBGY at Ajou University hospital, Suwon, Korea, between march, 1998 and march, 2000. Parity, activity, alcohol, smoking, age of menarche, and age of first and last pregnancy were recorded for prenatal information. Anthropometric measurements was checked at regular visits until 6 weeks after delivery and by telephone call at 6 months and 1 year postpartum. RESULTS: Mean age was 30.1 years old and mean body mass index was 21.1 kg/m2. Mean total weight gain during pregnancy was 13.6+/-4.63 kg and wide range was at third trimester. It shows that weight reduced gradually until 6 months postpartum but increased after that time. 1 year postpartum weight gain had high correlation(R=0.999, 0.01) with 6 months postpartum weight gain. Total pregnancy weight gain, weight retention on 6 week postpartum were not significantly correlated with 1 year postpartum weight gain. OR for becoming overweight on 1 year postpartum(> OR =5.2 kg) with excessive rate of gain on 6 months postpartum(> OR =2.9 kg) was 5.41(95% CI 2.20 13.31) adjusted by multiple logistic regression analysis(age, activity level, parity). OR for becoming overweight on 1 year postpartum with excessive rate of Total pregnancy weight gain(> OR =13.6 kg) was 4.48(95% CI 1.84 10.89) by multiple logistic regression analysis. CONCLUSION: 1 year postpartum weight gain had the correlation with only 6 months postpartum weight gain.