Little is known about the effect of HCV treatment on sexual risk behaviour among men who have sex with men (MSM) with HIV by treatment type (IFN-based vs DAA-based). MSM with HIV and recently acquired HCV infection enrolled in the observational MOSAIC cohort. Using data from 2009-2018, we evaluated risk behaviour through a validated HCV risk score (where ≥2 indicated high risk) and its individual risk behaviours. Levels of risk behaviour before, during and after treatment were modelled for each treatment episode using linear and logistic regression with Generalized Estimating Equations adjusting for DAA availability and number of re-infections. 140 MSM with a median age of 45 years (interquartile range=40-49) yielded 180 treatment episodes (n=131 IFN-based, n=49 DAA-based). Adjusted mean risk score before, during and after treatment was 2.4 (95% confidence interval (CI)=2.1-2.6), 0.9 (95%CI=0.8-1.0) and 1.7 (95%CI=1.5-1.8), respectively. Before treatment, no differences in mean HCV risk score or proportion of specific behaviours were found between the regimen groups. During treatment, MSM treated with DAAs had a higher average risk score and proportion of receptive condomless anal sex, sharing toys and unprotected fisting than those treated with IFN. After treatment, the proportion sharing straws were significantly higher in MSM treated with DAAs than IFN. MSM treated with DAAs, compared to IFN, had higher levels of HCV-related risk behaviour during treatment. The higher risk of HCV re-infection in the DAA-era underscores the need for ongoing HCV testing and behavioural interventions against HCV.