【Objective】 To research the impact of intrauterine mercury exposure on the neonatal physical development Index. 【Methods】 During the study period,the new-born babies delivered in our hospital were determined with the quantity of mercury in cord blood and in foetal hair immediately after birth.The new-born babies weight,length and head circumference were measured.According to gestational age,physical development index measurements that the new-baorn babies in 15 cities of China for comparison,and the cord blood mercury and fetal hair mercury values were analyzed in the percentile range for statistical analysis. 【Results】 The quantity of mercury of 2 316 paired cases was (2.02±1.94)μg/kg in cord blood,and(244.06±2.24)μg/kg in foetal hair.Cord blood mercury of head circumference in each group which was divided by percentile range (<P₁₀,P₁₀~P₂₅,P₂₅~P₇₅,P₇₅~P₉₀,>P₉₀) was 2.50±1.88,2.05±1.92,1.88±1.96,1.50±1.76,1.77±1.49 respectively,and fetal hair mercury in each group was 360.91±2.12,262.97±2.15,201.65±2.22,205.31±2.18,208.50±1.49 respectively.There were significant differences among cord blood mercury groups and fetal hair mercury groups (F₁=15.47,P₁=0.00;F₂=42.53,P₂=0.00).Cord blood mercury of weight in each group was 195.07±2.13,227.25±2.19,247.69±2.18,252.29±2.32,246.89±2.32 respectively,and there was significant difference among cord blood mercury groups(F=2.57,P<0.05).However,after removal of <P₁₀ group,there was no significant difference among the remaining four groups (F=0.91,P=0.44). 【Conclusion】 Intrauterine fetal mercury exposure not only affect in the future intellectual development,but also may adversely affect the newborn head circumference.