Objective To investigate the influence on anti-HCV antibody levels in spontaneous HCV seroconverters co-infected with HIV. Methods A retrospective study was conducted on people with a history of blood donation in Wangying Village,Shangcai County,Henan Province in 2009 and 2017. Accord-ing to the infection status in 2009,patients who were positive for anti-HCV antibody were divided into four groups:HIV-negative chronic HCV infection group (HCVc),HIV-negative spontaneous HCV clearance group (HCVr),HIV-positive chronic HCV infection group (HIV+HCVc),HIV-positive spontaneous HCV clear-ance group ( HIV+HCVr). All patients were followed up in 2017 and those who were lost to follow-up, received HCV treatment or were reinfected with HCV (only for those of HCV seroconverters) were excluded from this study. Altogether 167 patients met the inclusion criteria (HCVc:n=65;HCVr:n=34;HIV+HCVc:n=44;HIV+HCVr:n=24). A horizontal comparison of anti-HCV antibody levels among the above four groups in 2009 and a longitudinal comparison of changes in anti-HCV antibody in each group from 2009 to 2017 were respectively conducted. Results The horizontal comparison indicated that the levels of anti-HCV antibody were higher in chronic HCV-infected patients than in HCV seroconverters no matter whether they were co-infected with HIV or not (both P<0. 000 1). After comparison of anti-HCV antibody titers in 2017 and 2009,no significant changes were found in HCVc or HIV+HCVc group. The levels of anti-HCV antibody in HCVr and HIV+HCVr groups decreased significantly from 2009 to 2017 ( both P<0. 000 1). HIV+HCVr group showed a faster decline in anti-HCV antibody level than HCVr group (P=0. 003 9). Significant nega-tive correlations between the decline speed in anti-HCV antibody sample/cut-off ( S/CO) values and the initial anti-HCV antibody S/CO values (in 2009) were found in both HCVr (r=-0. 517 7, P=0. 001 7) and HIV+HCVr groups (r=-0. 753 2, P<0. 000 1). The decline speed in anti-HCV antibody in HIV+HCVr patients was found to be negatively correlated with their CD4+T cell counts in 2009 ( r=-0. 563 8, P=0. 004 1). Moreover,the seroreversion rate of anti-HCV antibody in patients of the HIV+HCVr group was higher than that of HCVr group (P=0. 027 5). Conclusion HIV co-infection can accelerate the decline of anti-HCV antibody in spontaneous HCV seroconverters. This study indicates that in a large-scale retrospective epidemiological investigation especially for HIV-infected populations, the prevalence of anti-HCV antibody may be underestimated.