Aim To study the association between angiotensin converting enzyme (ACE) gene polymorphism and ACE activity,angiotensin Ⅱ (AngⅡ) in coronary artery disease patients. Methods The serum ACE activity and plasma AngⅡ level in 76 patients with coronary artery disease and 68 healthy subjects were measured. The relation between serum ACE activity and plasma AngⅡ level was analyzed by linear regression. Results The serum ACE activity and plasma AngⅡ level were similar in coronary artery disease and control groups. But the serum ACE activity in different genotypes was significantly different in the two groups. The serum ACE activity in DD genotype (homozygotes for the deletion) was markedly higher than in ID genotypes (heterozygotes) and II genotypes (homozygotes for the insertion). The plasma AngⅡ level was similar in different genotypes in the two groups. No correlation was found between serum ACE activity and plasma AngⅡ level. Conclusion The ACE gene insertion/deletion polymorphism is the important factor that influenced the serum ACE activity. However it has no influence on plasma AngⅡ level. There is no relationship between the serum ACE activity and plasma AngⅡ level. The findings suggest the mechanism that ACE insertion/deletion polymorphism contribute to the generation or development of coronary artery disease is not completed by increasing plasma AngⅡ level.