Abstract: Objective To assess the genetic and environmental influences on skinfold thickness and body composition of children and adolescents in different development periods.Methods The triceps and subscapular skinfolds were measured and the body composition were estimated by using Changling's and Brozek's models in a total of 376 twin pairs of Han nationality,including 245 monozygotic(MZ)and 131 like-sex dizygotic(DZ)twin pairs aged 6 to 18 years.Model-fitting method with Mxpackage was performed to evaluate the proportion of variance components and to analyze the effect of sex,age and development period on the skinfold thickness and body composition.Results The estimated heritabilities of each item were from 0.59 to 0.87 after adjusting for age.The heritabilities of triceps skinfolds,subscapular skinfolds,sum of triceps and subscapular skinfolds and body fat percent were the lowest in pre-adolescent period in the boys(0.55,0.62,0.53,0.51,respectively)and the lowest in late-adolescent period in girls(0.53,0.43,0.24,0.40,respectively).In the course of adolescence,the heritabilities of lean body mass increased steadily in both boys and girls.Conclusion The skinfold thickness and body composition of the children and adolescents are mainly influenced by genetic factors and the effects of the age,gender and the development periods should be considered too.