Abstract: Objective To analyze genetic and environmental influences on physical measurements of school-age twins, and the effects of sex and age.Methods A total of 297 tw in pairs,including 167 monozygotic(MZ),90 like-sex and 40 opposite-sex dizygotic(DZ)twin pairs,aged 6-12 years were investigated.The measurements inculded hight,sitting hight, weight,chest circumference,triceps skinfold,subscapular skinfold,and suprailiac skinfold.Model-fitting by Mx package was performed to evaluate the effects of heredity and environment.Results All of the physical measurements were related to age except triceps skinfolds was associated with age and sex.The genetic model for all items was ACES.Genetic variant component was higher than that of environment for each item.Common environmental effect on skinfolds in the boys was higher than that in the girls,and age variant components of skinfold(0.02-0.17)were lower than those of other items (0.35-0.74).After adjusting for age,the heritabilities of hight,sitting hight,weight,chest circumference,triceps skinfold, subscapular skinfold,and suprailiac skinfold were 0.80,0.76,0.53,0.72,0.51,0.56,and 0.51 in the boys and 0.83,0.79,0.73,0.66,0.87,0.86,and 0.83 in the girls,respectively.The female's heritabilities of weight and skinfold were higher than those of the male's.Conclusion The body physical measurements of school-age children are mainly influenced by the genetic factors but the effects of the age and gender on the heritability should be considered too.