Abstract: Objective　To investigate the changes of serum leptin and bone speed of sound (SOS) with gestational age (GA) and relationship between leptin and bone SOS in appropriate-for-gestational-age (AGA) neonates. Methods A total of 65 AGA neonates were recruited and divided into three groups according to their gestational age: preterm infant (GA 31-34 w, 14 cases), late preterm infant (GA 34-37 w, 13 cases), and full-term infant (GA ≥ 37 w, 38 cases). Anthropometric parameters, including birth weight, length, leg length, skin fold thickness were measured in all the subjects, and the neonatal nutritional status and body fat content were evaluated by Ponderal Index (PI) and Weststrate equation (F%) respectively. Serum leptin concentration and tibial SOS were measured within 7 days after birth. Results There were significant differences in GA (F=140.199, P<0.001), birth weight (F=47.042, P<0.001), birth length (F=46.877, P<0.001), leg length (F=17.543, P<0.001), PI (F=11.898, P<0.001) and F% ( F=21.955, P<0.001) among three groups. Serum leptin and tibial SOS were significantly different among these groups ( F=49.724, 20.052 respectively, P<0.001), and both of them were positively correlated with gestational age and birth weight (P<0.01). In addition, leptin was positively correlated with tibial SOS, but the correlation disappeared after adjustment for GA and anthropometry. According to the multivariate forward stepwise regression analysis, tibial SOS was found to be significantly positively associated with gestational age and birth weight in the three groups. Conclusions Both bone SOS and serum leptin are significantly correlated with gestational age and birth weight in AGA neonates, and leptin is related with but not the independent direct predictor of bone SOS.