Abstract: Objective To discuss the effect of different specimens pretreatments on determination of angiotensin I and Ⅱ levels. Methods A total of 40 blood samples were collected and used by three different treatment methods(method 1:blood was drawn into EDTA-K₂ anticoagulated vacuum tube, then added with enzyme inhibitor immediately. method 2:enzyme inhibitor was added to the EDTA-K₂ anticoagulated vacuum tube first, then mixed with blood. method 3:the enzyme inhibitor was added at one hour after blood drawn was placed in the refrigerator), after separation of plasma, the levels of AⅠ and AⅡ were detected by chemiluminescence. Results The results of AⅠ and AⅡ bymethod 2 were not significantly different from those by the method 1.But the levels were significantly descended using method 3 as compared with method 1. Conclusion There were inhibitory effects of enzyme inhibitor on the conversion among AⅠ,AⅡ and AⅢ. Adding enzyme inhibitor first makes no significant difference to detection results from adding it after blood drawing and helps not to forget to add the inhibitor.