Objective: To investigate the status of infant birth weight in Nanjing area and explore potential risk factors of low birth weight and macrosomia. Methods: A multi-stage sampling method combined by stratified sampling and cluster sampling was used and five districts and town streets of Xuanwu and Luhe area were respectively taken as the program field. Total 3305 subjects of live birth from 2002 to 2004 were chosen as retrospective observation objects with the questionnaire survey. The information of maternal age,weight,educational level,gestational age,gravidity and neonatal birth weight etc. were collected according to the maternal health card provided by local maternity and child care center. Results:① The average birth weight of the neonates in Nanjing in the year 2002-2004 was 3 373.76 ± 466.23 g. The incidence rate of low birth weight was 1.4% and that of macrosomia was 6.8%. ② The average birth weight and height of the neonates in Xuanwu district(3 505.71 ± 541.92 g,49.69 ± 3.37 cm) were significantly higher than those in Luhe district (3 293.09 ± 392.01 g,48.63 ± 2.70 cm)(P < 0.05). The birth weights of male were significantly higher than those of female in Xuanwu and Luhe districts,respectively (both P < 0.001). ③ The birth weight of the neonates of 2004 was significantly higher than that of 2003,and the birth weight of female of 2003 was lower than that of 2002 (P < 0.05) in Xuanwu district,whereas no statistical differences of birth weight was found between the years of 2002,2003 and 2004. ④ With the increase of gestational age,birth weights of the neonates elevated significantly in different districts and different gender(P < 0.01). Additionally,birth weights of female linearly increased with the increase of pregnancy age (F = 3.887,P < 0.01). Conclusion: The results suggest that there were significant rural-urban difference and sex difference for birth weight in Nanjing City. Birth weight arises significantly with the increase of gestational age and pregnancy age.