Abstract: Objective：To investigate the effect of the methylation of apolipoprotein A5 ( apo A5 ) gene on the expression level of apo A5 in male patients with hypertriglyceridemia (HTG) and acute myocardial infarction (AMI). Methods：Eighteen male patients with HTG and AMI were included in the case group, while 18 with HTG and carotid atherosclerosis (As) in the control group. The DNA methylation changes in peripheral blood of two groups of patients were detected by the Illumina Human Methylation 450K BeadChip, and the difference of apo A5 methylation between the two groups was compared by the bioinformatic analysis. In addition, the mRNA level of apo A5 and the protein level of plasma apo A5 were determined by real-time fluorescence quantitative PCR (RT-PCR) and ELISA, respectively. Results：The genome wide methylation screening showed that the apo A5 gene was hypermethylated in the case group when compared with the control. The mRNA and protein levels of apo A5 in the case group were significantly lower than that of the control group ［(0.037±0.016) vs(1.000±0.093), t=18.970, P<0.05; (156.6±16.8) μg/L vs (197.3±32.3） μg/L, t=2.502, P<0.05］. Conclusion：The low mRNA and protein levels of apo A5 in male patients with HTG and AMI may be related to the increased methylation of apo A5 gene, and the abnormal methylation of apo A5 gene may be involved in the progress of atherosclerosis in HTG patients.