BACKGROUND: Coronary artery disease is a leading cause of death in developed countries. On the other hand, increased level of CRP has been seen in atherosclerosis. According to this finding, we decided to conduct this study to assess the relationship between CRP and complex lesions of coronary arteries in patients with unstable angina.    METHODS: In this analytical cross sectional study which was conducted in 2007 in Chamran hospital, samples were collected using simple sampling and included 80 patients who referred to the hospital due to angina pectoris, had the diagnosis of unstable angina and were candidates of angiography. At first, a questionnaire was filled for each patient including demographic factors and their medical history. Then a blood sample was taken to assess level of CRP, FBS, and lipid profiles. The results of angiographic studies were considered by three cardiologists and abnormal patients were classified into simple and complex groups according to Ambrose criteria. Data was analyzed using SPSS version 15, t-student and chi-square tests.    RESULTS: Mean age of samples was 58.27 ± 6.23 years old. Considering the risk factors, most simple and complex lesions happened in obese patients however the only significant difference was observed in BMI between two groups (p < 0.05). Mean level of CRP in the population under study was 6.05 ± 4 mg/dl which was 1.37 ± 2 and 8.01 ± 6 in simple and complex groups respectively (p < 0.05). CRP mean was significantly higher in the group with complex lesions, less than 1 mg/dl in simple lesion and more than 4 mg/dl in complex lesions.    CONCLUSION: According to our findings, there is a significant difference considering CRP level in unstable angina patients who have complex lesions compared with simples ones. As complex plaques are more susceptible to develop coronary events, patients with a higher probability of complicated lesions can be screened.      Keywords: CRP, Simple and complex lesion, Unstable angina, Angiography.