Objective：To determine the correlation between birth weight and the level of insulin-like growth factor(IGF)-I, -II and insulin-like growth factor binding protein(IGFBP)-3 in amniotic fluid at second trimester and to evaluate possibility whether the levels of IGF-I, II and IGFBP-3 could predict birth weight. Methods：Sixty-seven samples of amniotic fluid in second trimester were analyzed for IGF-I, IGF-II, and IGFBP-3 by radioimmunoassay. Newborn birth weights were stratified arbitrarily as <25th percentile, 25-75th percentile, and >75th percentile. Linear regression analysis and Kruskal-Wallis test were used in well appropriately for statistical analysis. Results：The level of IGF-I showed positive correlation with birth weight. However, the levels of IGF-II and IGFBP-3 showed no significant correlation with birth weight. The level of IGF-I were significantly different among these groups. However, the levels of IGF-II and IGFBP-3 were not significantly different among these groups divided by the birth weight percentile. Conclusion：The levels of IGF-I in amniotic fluid at second trimester may be useful marker in predicting birth weight.