Background: Limited data are available on hepatitis C virus (HCV) infection in persons who inject drugs (PWID) in South Korea. The present study aimed to investigate the seroprevalence of HCV antibodies, risk factors for HCV seropositivity, and HCV treatment status in PWID between January 2012 and May 2022. Methods: We retrospectively reviewed the medical records of 418 drug users who underwent HCV antibody testing in three hospitals caring for 90% of known PWID in South Korea, of whom 373 were PWID. Results: The HCV seroprevalence was 39.7% (148/373) in PWID vs. 6.7% (3/45) in noninjection drug users (P < 0.001). Age ≥ 40 years, hospital type (58.2% in the prison hospital vs. 34.0% in the private hospital), and enrollment year (68.2% in 2012–2014 vs. 30.0% in 2021–2022) were independently associated with HCV seropositivity. Among the HCVseropositive PWID, 90.5% (134/148) were diagnosed with HCV infection; however, only 6.8% (10/148) received HCV treatment. The hepatitis B virus surface antigen and human immunodeficiency virus antibody positivity were 4.0% (14/352) and 1.9% (6/317) in tested PWID, respectively. Conclusion The HCV seroprevalence in PWID was 39.7% with a very low treatment rate, which prompts active measures to test and treat PWID for HCV infection in South Korea.