One hundred and sixty-nine patients with posttransfusion hepatitis (PTH) were investigated for etiology with serological and PCR methods. Our result showed that HCV was the major causative agent of PTH in this study. A part of patients (24/169) were also HBV markers positive. Three patients were negative for all detected viral markers, looking forwards to progressive study. Anti-HCV was detectable from 7 days to one year after onsetting of clinical symptoms, average time 54.62 days. HCV RNA could be detected in early time of HCV infection ( 6 to 20 days later), average time 8.72 days. A follow-up study of 84 patients showed that all patients remained anti-HCV positive during the observation for 1.5 -- 3 years, but their HCV viremia had three forms: transient, persistent or intermittent. The interaction between HCV and HBV by their superinfection was unknown, awaiting further study.