OX40 and OX40L, members of the tumor necrosis factor receptor superfamily, are costimulatory molecules involved in the activation and proliferation of T lymphocytes. OX40L plays an important role in the process of atherosclerosis, and variants of OX40/OX40L are associated with myocardial infarction in European populations. Our study examined 235 patients with acute coronary syndrome (ACS) and 220 controls and sought to establish whether polymorphisms in OX40/OX40L are associated with atherosclerosis or myocardial infarction in the Han Chinese population. OX40 rs17568A/G, rs2298212A/G, and OX40L rs3850641A/G polymorphisms were genotyped using the polymerase chain reaction-restriction fragment length polymorphism method. The results showed that carriers of the G allele of rs17568A/G had a significantly increased risk of ACS (p = 0.023, adjusted odds ratio = 1.72, 95% confidence interval = 1.08-2.75) after adjusting for age, sex, diabetes, hypertension, and lipids. No significant association between rs2298212A/G or rs3850641A/G and the risk of ACS was found in this study. In conclusion, OX40 gene polymorphism may be associated with a risk of ACS in the Han Chinese population, although the association between OX40L polymorphisms and ACS requires further investigation.