Five years crossbreeding experiment was preformed involving two synthetic rabbit lines of APRI (A) and Moshtohor (M) where bucks of APRI line and does of Moshtohor line were used to produce F₁ crossbreds (½A½M), followed by inter-se mating to obtain F₂ crossbreds (½A½M)². PCR-RFLP technique was used to detect the SNP genotyping of MSTN gene in APRI and Moshtohor lines and their progenies of F₁ and F₂ crossbreds and to detect the molecular associations between SNP genotypes of MSTN candidate gene and growth traits using FspBI restriction enzyme. Two genotypes of MSTN gene were detected (TT and TA) in each separate genetic group. The variance components estimated by Gibbs Sampling were used to solve the mixed model equations using the PEST software, getting the solutions for genetic groups effects along with the solutions for other fixed effects. Then, the generalized least-square means (GLM) for the two genotypes of the MSTN gene were estimated using the PEST software. The GLM obtained for body weights at 4, 6, 8, 10 and 12 weeks of age in both crosses of ½A½M and (½A½M)² were higher than those of their parental lines of APRI and Moshtohor. But, APRI-line rabbits were nearly similar in body weights to Moshtohor line rabbits at 8, 10 and 12 weeks of age. The effective numbers of alleles (N_e) were 1.26, 1.08, 1.11 and 1.37 in APRI line, Moshtohor line, ½A½M and (½A½M)² crosses, respectively. High degrees of similarity were detected between the numbers of expected and observed genotypes in all genetic groups and therefore these genetic groups were in Hardy-Weinberg equilibrium (HWE) for MSTN gene. The values of polymorphic information content (PIC) were low and ranged from 0.073 in Moshtohor line to 0.235 in (½A½M)² cross. The genotypic frequencies of TT genotype of MSTN gene were high in all genetic groups (0.68 to 0.92). The allelic frequency recorded for T allele was much higher than for A allele. The heterozygosis for MSTN gene in all genetic groups were low or moderate, ranging from 0.079 to 0.323 for the observed heterozygosity (H_O) and 0.076 to 0.271 for the expected heterozygosity (H_e). The reductions in heterozygosity due to inbreeding (F_IS) in all genetic groups were low. In different genetic groups, both TT and TA genotypes of MSTN gene were found to be significantly associated with most body weights and gains at different ages. In APRI line and (½A½M)² cross, TT genotype was positively associated with an increase in most body weights. In Moshtohor and ½A½M cross, TA genotype was positively associated with heavy body weights. High means for TT and TA genotypes of MSTN gene in ½A½M and (½A½M)² crosses were recorded and showing strong positive associations of both TT and TA genotypes of MSTN gene with most body weights and gains.