Association between T2DM and vitamin D deficiency has been reported in many epidemiologic studies. 24-hydroxylase encoded by CYP24A1 is the enzyme that degrades the active vitamin D metabolite. Variation in CYP24A1 may be associated with T2DM. This study investigates the association between rs2248359 in CYP24A1 and T2DM by a family-based association test (FBAT) and in a case-control study. The FBAT results revealed that there was transmission disequilibrium for allele T in both additive model (Z = 2.041, P = 0.041227) and dominant model (Z = 2.722, P = 0.006496). Results of the case-control study suggested that rs2248359 may be a risk factor for female T2DM (P = 0.036) but not for male T2DM (P = 0.816). Furthermore, excessive transmission of allele T in T2DM offspring was observed compared with the non-T2DM offspring (OR 1.392; 95%CI 1.024-1.894; P = 0.035). In addition, combination of maternal CT and paternal CC genotypes had significant synergistic effect on obtaining CT genotype for offspring with T2DM (OR 6.245; 95%CI 1.868-20.883; P = 0.004). Besides, lower level of 25(OH)D in T2DM offspring with genotype CT was observed as compared with the non-T2DM offspring (P = 0.013). These data suggest that maternal transmission disequilibrium of allele T may be a risk factor for T2DM and vitamin D deficiency in T2DM offspring.