Type 2 diabetes mellitus (DM) is associated with significant abnormalities of lipoprotein metabolism and coronary heart disease (CHD). The most commonly recognized lipid abnormality in type 2 DM is hypertriglyceridemia, which is known to be an independent risk factor for CHD in diabetics. The -1131T-->C polymorphism found in the newly identified apolipoprotein A5 ( APOA5 ) gene has been found to be associated with elevated plasma triglyceride (TG) concentrations in different racial groups. In this study, DNA samples from 155 control subjects, 172 type 2 diabetics and 113 type 2 DM patients with CHD were analyzed to examine the influence of APOA5 1131T-->C polymorphism on plasma lipids and the susceptibility to CHD in type 2 diabetics. The frequency of the APOA5 -1131C allele in the DM+CHD group was significantly higher than that of control subjects (37.2% vs. 27.7%, p=0.021). The distribution of the APOA5 -1131T-->C genotypes (TT, TC and CC) was 36.3%, 53.1% and 10.6% in type 2 DM patients with CHD, and 53.6%, 37.4% and 9.0% in controls, respectively (p=0.018). The frequencies of alleles and genotypes in type 2 diabetics were not significant compared to controls. In controls, plasma TG concentrations in subjects with the TT genotype were significantly lower than in those with TC/CC (0.92, 1.28 and 1.35 mmol/L for TT, TC and CC, respectively; p = 0.003 by ANOVA). These data suggest that the APOA5 -1131T-->C polymorphism might play a role in elevated plasma TG levels in type 2 diabetic patients in the Chinese population.