OBJECTIVE To investigate the variations of OX40 (tumor necrosis factor receptor superfamily, member 4) and its ligand OX40L genes and their relationships with serum lipids and apolipoproteins (apo) levels in Chinese healthy individuals and patients with endogenous hypertriglyceridemia (HTG) in the Chengdu area. METHODS The genotypes and allele frequencies of the rs3850641 and rs17568 polymorphisms in the OX40L and OX40 genes were assayed by polymerase chain reaction and restriction fragment length polymorphism. RESULTS In the case-control study, which included 126 HTG subjects and 206 normal control subjects, the frequencies of the G allele at the rs3850641 site and the G allele at the rs17568 site in the patients were similar to those observed in the controls. In the HTG group, subjects with G allele carriers of the rs3850641 site had lower serum high-density lipoprotein cholesterol and apo AI levels as compared to those of genotype AA. In the case group, subjects with G allele carriers of the rs17568 site had higher serum low-density lipoprotein cholesterol (LDL-C) levels, while controls had lower serum total serum cholesterol and LDL-C levels. CONCLUSIONS These results suggest that the rs3850641 and rs17568 polymorphisms in the OX40L and OX40 genes are associated with some of the lipid and lipoprotein variations in subjects with endogenous HTG and/or in the general population of Han Chinese.