Abstract: A total number of 307 pairs of twin of the same sex aged 6 to 14 were investigated. The result shows that the proportion of twins among the primary pupils was 0. 39%. The proportion of MZ twins was 54. 12%, while the proportion of DZ twins was 45. 88%. The skeletal age, height and weight were all genetically determined, with a heretability of 79. 3e, 36. 5% and 78. 2% respectively. The genetic factors might influence these indexes differently in different age groups. Various environmental factors lasting for a long time have greater effect on height and weight than on skeletal age.

Key words: Twin; Genetics; Skeletal age; Height; Weight