Background Aspirin is widely used in the secondary prevention of coronary artery diseases, including myocardial infarction, stroke, and vascular related deaths. However, the antiplatelet effect of aspirin appears to be variable and aspirin resistance (AR) is currently still controversial for Chinese patients. The aim of this study was to describe the prevalence of AR, and identify possible risk factors associated with a lack of response to aspirin treatments in patients with unstable coronary artery disease.Methods Platelet function tests with arachidonic acid (ARA) and urinary 11-dehydro-thromboxane B2 (11-DH-TXB2) concentrations were performed in 262 patients with unstable coronary artery disease who had not been taking aspirin before admission. ARA induced platelet aggregation and 11-DH-TXB2 were detected to evaluate the functional and biochemical responses to aspirin before and on days 1, 4, and 10 after aspirin administration. Six-month follow-up was completed in patients who developed AR to evaluate the effect of aspirin in a long-term treatment. GP1 Bα (C1018T), PI(A1/A2), P2Y1(A1622G), TBXA2R (T924C) were also detected to evaluate the influence of genetic variant on aspirin responsiveness.Results A total of 8.8% of patients were indentified as AR at the first day after aspirin treatment. The level of urine 11-DH-TXB2 in the AR group was higher compared to non-AR group (P ＜0.05). There was no relationship between ARA induced platelet aggregation and urinary 11-DH-TXB2 levels (r=0.038, P=0.412). The results of DNA sequencing showed that TBXA2R-924TT homozygotes had a significantly high rate of AR. Logistic regression demonstrated that diabetes was an independent risk factor of AR.Conclusions In the beginning period of administration, aspirin was not a sufficient factor that inhibits platelet aggregation. TBXA2R-g24T allele was involved in AR. Diabetes was an independent risk factor of AR.