Objective:To evaluate the utility of HCVcAg detection system in clinical diagnosis of hepatitis C infection. Methods:HCVcAg and anti-HCV in sera of 214 hepatitis C patients,60 health control and 40 patients with other hepatic disease were detected by ELISA,and sera HCV RNA was measured by real-time quantitative PCR. Meanwhile,the sera from 78 patients with HIV infection were screened for HCV infection. Results:162 patients (75.7%) were HCVcAg positive in 214 hepatitis C patients. The positive ratio of HCVcAg increased with the HCV RNA copies. The HCV RNA copies were highly related with the HCVcAg with HCV RNA copies over 106/ml. Of 78 samples with HIV,16 were HCV RNA positive,15 were HCVcAg positive,9 were anti-HCV positive. Conclusions:HCVcAg is a serological marker for early identification of HCV. The measurement of HCVcAg significantly shortens the window period of HCV detection,especially for the individuals with negative anti-HCV detection results who use immunosuppressant,and is substituted for HCV RNA detection in where PCR cannot be carried out.