Smoking is prevalent among individuals receiving methadone treatment. Reducing smoking among this population is needed as smoking is a leading cause of morbidity and preventable death. Smoking cessation interventions for persons receiving medication for opioid use disorder have yielded small changes in abstinence. Bupropion-SR was developed as an anti-depressant medication and is a first-line medication for smoking cessation. There is limited research on the effectiveness of bupropion-SR on smoking cessation among individuals receiving medication for opioid use disorder. This study is a secondary analysis of N = 72 adults enrolled in methadone treatment who endorsed smoking cigarettes. Participants were randomized to receive bupropion-SR 150 mg twice-daily (n = 35) or placebo (n = 37) in the primary study that examined bupropion-SR on cocaine use outcomes over a 30-weeks. Mixed model analyses examined secondary changes in self-reported cigarettes smoked, a self-reported measure of nicotine dependence, and quantitative urinary cotinine values. The longitudinal analysis of self-reported daily cigarettes identified no main effects of group and week however a significant interaction between group and week revealed that persons receiving bupropion-SR group reported less smoking early in the intervention. Longitudinal evaluation of changes in urinary cotinine revealed a significant main effect of week but no main effect of group or group x week interaction. Data suggest that bupropion-SR significantly decreased the number of self-reported cigarettes smoked relative to placebo and reduced nicotine dependence severity by the end of the study. Follow-up studies are needed as these decreases were not identified throughout the full study period or at termination.