To evaluate the efficacy and investigate the influencing factors of the interferon (IFN) retreatment for patients with chronic hepatitis C relapsed after a previous IFN treatment.A retrospective study was designed to analyze the retreatment with IFN of 60 relapsed chronic hepatitis C patients. All patients were from a randomized, opened and multi-center clinical trial about the efficacy and security of PEG-IFNalpha-2a compared to CIFNalpha-2a in the treatment of chronic hepatitis C in China. There were 35 patients treated with PEG-IFNalpha-2a and 25 with CIFNalpha-2a. The main parameter to evaluate the efficacy was sustained viral response (SVR) rate. The influence of viral concentration in serum, genotype and drug categories on the responses to IFN were analyzed.For all the patients, the end of treatment virus response (ETVR) and SVR rates were 55.00% and 35.00% respectively. ETVR rate of PEG-IFNalpha-2a was significantly higher than that of CIFNalpha-2a (74.29% and 28.00% respectively, P < 0.01). SVR rate of PEG-IFNalpha-2a was also markedly higher than that of CIFNalpha-2a (45.71% and 20.00% respectively, P < 0.05). However, there was no significant difference between the high and low viral load groups. Among the patients with genotype 1, ETVR and SVR rates of PEG-IFNalpha-2a (75.00%, 45.83%) were significantly higher than those of CIFNalpha-2a (22.22%, 11.11%), (P < 0.01, P < 0.05 respectively), but in patients with genotype non-1, there were no such differences between the two groups.Some relapsed patients were not responsive to the IFN retreatment. The efficacy of PEG-IFNalpha-2a was superior to CIFNalpha-2a. The conventional IFN was not suggested to be used in the relapsed cases with genotype 1. The viral load was not associated with the efficacy of IFN retreatment.