As one of the problematic behaviors in patients with major depressive disorder (MDD), excessive online game play (EOP) has been reported in a number of recent studies. Bupropion has been evaluated as a potential treatment for MDD and substance dependence. We hypothesized that bupropion treatment would reduce the severity of EOP as well as depressive symptoms. Fifty male subjects with comorbid EOP and MDD were randomly assigned to bupropion + education for internet use (EDU) or placebo + EDU groups. The current study consisted in a 12-week, prospective, randomized, double-blind clinical trial, including an eight-week active treatment phase and a four-week post treatment follow-up period. During the active treatment period, Young Internet Addiction Scale (YIAS) scores and the mean time of online game playing in the bupropion group were greatly reduced compared with those of the placebo group. The Beck Depression Inventory (BDI) scores in the bupropion group were also greatly reduced compared with those of the placebo group. During the four-week post-treatment follow-up period, bupropion-associated reductions in online game play persisted, while depressive symptoms recurred. Conclusively, bupropion may improve depressive mood as well as reduce the severity of EOP in patients with comorbid MDD and online game addiction.