Background/Aims: Chronic hepatitis C virus (HCV) infections put patients at risk of serious liver disease and adversely affects patient quality of life (QoL). MOSAIC (International Multicenter Prospective Observational Study to Evaluate the Epidemiology, Humanistic and Economic Outcomes of Treatment for Chronic Hepatitis C Virus) was a prospective, non-interventional, international, multicenter study that aimed to describe the epidemiology of the infection, the impact of the infection on health-related QoL (HRQoL) and daily activities, and healthcare resource use related to HCV and treatment. Here, we present the results on HRQoL and daily activity impairment in consecutively enrolled South Korean patients treated with interferon (IFN)-containing regimens prospectively followed for up to 48 weeks. Methods: General HRQoL, HCV-specific HRQoL, perceived health state, and work/general activity impairments were measured using the EuroQoL 5-dimension 5-level (EQ-5D-5L), HCV patient-reported outcomes (HCV-PRO), EQ-5D Visual Analog Scale, and Work Productivity and Activity Impairment questionnaires, respectively. Results: Thirty-three of the 100 enrolled patients initiated IFN-based treatment, with an intended duration of 24 weeks for 20 patients and 48 weeks for 12 patients; this information was missing for one patient. Fourteen patients (42.4%) prematurely withdrew. After treatment initiation, IFN-treated patients showed a trend towards deterioration of both general (baseline: 0.87±0.103, week 4: 0.77±0.153) and HCV-specific (baseline: 76.2±19.5, week 4: 68.2±22.3) HRQoL. The scores recovered somewhat towards the end of treatment (EOT) (0.84±0.146 for EQ-5D-5L and 70.8±21.9 for HCV-PRO). The perceived health state and work/general activity impairment displayed similar temporal patterns. Conclusions Initiating IFN-based treatment prompted some deterioration in general and HCV-related HRQoL, accompanied by impaired daily activities and most work productivity measures; however, the HRQoL and productivity scores improved towards the EOT. HRQoL impairment upon treatment initiation likely contributed to treatment discontinuation.