Abstract: Objective To study the prevalence rate and heritability in the first degree relatives of type 2 diabetes mellitus (DM)in Shenyang,to estimate the effect of genetic factors in type 2 diabetes mellitus.Methods On the basis of the survey of type 2 diabetes mellitus in hospital population and urban community population of Shenyang(203 cases and 201 controls),a case-control study was carried out.Chi square test was used for data analysis and the Falconer was used to calculate the heritability.Results The family history was the risk factor of type 2 diabetes mellitus(OR=5.89).The prevalence rate in the first degree relatives of index cases was 6.76%,higher than the controls of 1.27%,the risk ratio(RR)was 5.32(95% CI=3.54~7.99,).The heritability was 56.88%.Conclusion Genetic factors make an important role in type 2 diabetes mellitus,and higher genetics susceptibility were found in the first degree relatives of DM,on whom prevention and treatment for DM should be focused.