Background: Previous studies in patients with hepatitis C virus (HCV)/HIV coinfection have shown that the presence of GBV-C is associated with significantly less compensated and decompensated cirrhosis, and an improvement in cirrhosis-free survival. Objectives: This study aimed to describe the effect of GBV-C in patients with chronic hepatitis C and HIV coinfection. Patients and Methods: We retrospectively studied 105 injecting drug users with chronic hepatitis C and HIV coinfection and 72 patients with chronic HCV mono-infections. Plasma samples were tested for GBV-C RNA with primers to the 5'untranslated region gene. HIV and HCV viral load, CD4(+) and CD8(+) cell count, and the levels of alanine aminotransferase (ALT) and aspartate aminotransferase (AST) were tested in all patients. Results: GBV-C RNA was identified in 34 (32.38%) of the patients with HIV/HCV coinfection, and in 24 (33.33%) of the patients with HCV mono-infection. GBV-C infection was associated with significantly lower ALT and AST levels in patients with chronic hepatitis C and HIV coinfection, but not in those HCV mono-infections. The presence of GBV-C infection was not correlated with CD4(+) and CD8(+) cell count, gender, age, HIV load, HCV load, and HCV genotype. Conclusions: This study found that GBV-C infection has a high frequency among injecting drug users with HIV/HCV coinfection and HCV mono-infection in Yunnan, China. In patients with chronic hepatitis C and HIV coinfection, GBV-C RNA was associated with significantly lower ALT and AST levels, suggesting a beneficial effect of GBV-C infection on chronic hepatitis C.