Balanced body composition plays an important role in maintaining the health of the body. Body composition is affected by both genetic and environmental factors. Dopamine is involved in the regulation of food intake, movement and cognition, dopamine D3 receptor (DRD3) plays a key regulatory role in dopamine pathway, and then plays a role in feeding function, thus may affect body composition. In order to understand the influence of genetic and environmental factors on body composition of twins, and to explore the correlation between single nucleotide polymorphism (SNP) of DRD3 gene and body composition, the triceps skinfold (d₁), subscapular skinfold (d₂) and suprailiac skinfold (d₃) and body mass(m) were measured in 160 pairs of twins aged 4-12 years, d₄(d₁+d₂), d₅(d₂/d₁), body fat percentage(P_f), lean body mass(m_l) were calculated. The whole genome DNA was extracted from oral swab. The zygosity was determined by Amp FISTER SinofilerPlus kit. Four SNPs of DRD3 gene were detected by SNapshot technique. The heritability of each index was estimated by Mx software. The association between SNP of DRD3 gene and each index was analyzed by generalized estimating equation (GEE) model. After adjusting for the age effect, except for some indexes (d₃, m_l), the heritability of boys and girls in preschool is generally low, the heritability of some indexes (d₂, d₄, P_f, m_l) showed some gender differences. There were association between d₂ and rs32409, rs226082 (P<0.05), between d₃ and rs2134655, rs226082 (P<0.05), between d₅ and rs2134655, rs167771 (P<0.05), between P_f and rs226082, rs167771 (P<0.05), between m_l and rs2134655, rs226082 and rs167771(P<0.05) respectively. The results showed that both genetic and environmental factors affected the body composition development of children, but there may be some developmental stages and gender differences in genetic effects. SNPs of DRD3 gene may be related to body composition of children.