Most of the studies on sitting height(h), lower limb length(L), and their ratio(h/L) were based on non-twin populations. To understand the relative influence of genetic and environmental factors on the sitting height, lower limb length and the ratio of sitting height to lower limb length of children and adolescents, we measured their standing height(H) and sitting height of 796 pairs of twins aged 6-18 years old, and computed their lower limb length and the ratio of h and L. Genetic analyses was done using structural equation models. After adjusting the age, the degree of heritability(d) of h and L in the 15-18 years old group(0.63≤d<0.78) was higher than that for h and L in other younger age groups(0.31≤d<0.68) in both sexes; the heritability of h/L in boys(0.16≤d<0.46) and girls (0.21≤d<0.57) was low except for that of h/L in girls (d=0.84) aged 9-11 years. Our study findings show that common and unique environmental factors exerted a stronger influence on these anthropometric measurements in children and adolescents aged 6-14 years, suggesting during the period of rapid growth, their h, L and h/L are more sensitive to environmental effects. When individuals approached maturity, the genetic effects became stronger.