Abstract: A population based case-control family study including 654 pedigrees(363 index cases and 291 population controls) was carried out to explore the role of genetic agent on the developmentof type 2 diabetes mellitus(DM). The results showed that the cumulative incidence rate of the first-degree relatives in cases was 3.94%, significantly higher than that in controls(1.10%). The relative risk(RR) of DM inprobands'pedigrees was 3.62(Χ₂2 = 36.5, P< 0.001). The same results were also found in their female and male relatives. The cumulative incidence rates and RR among relatives of probands aged less than 55 year sold were significantly higher than that of probands aged more than 55 years old. Results from binominal distribution analysis showed that there was significant famillial aggregation in the occurance of DM in the first-degree relatives in cases. Hert ability in the first-degree relatives of diabetes probands was 40.6%(male 42.6%, female 38.6%). These gregation ratio of DM was 0.032, which was significantly lower than 0.25, and met the features of polygenic diseases.