Objective: To evaluate the relative impact of three brief therapist-supported internet-delivered emotion regulation treatments for maladaptive anger (mindful emotion awareness [MEA], cognitive reappraisal [CR], and mindful emotion awareness + cognitive reappraisal [MEA + CR]) and to test whether baseline levels of anger pathology moderate treatment outcome. Method: Treatments were evaluated in a randomized controlled trial. In total, 234 participants (59% female; mean age = 41.1, SD = 11.6) with maladaptive anger were randomized to MEA (n = 78), CR (n = 77), or MEA + CR (n = 79). Self-reported primary and secondary outcomes were followed up at primary endpoint, 3 months after treatment termination (88% retention). Primary outcomes were also assessed weekly during a prolonged baseline phase (4 weeks) and an active treatment phase (4 weeks). Results: At the primary endpoint, the MEA + CR was superior in terms of anger expression (d = 0.27 95% confidence interval, CI [0.03, 0.51]), aggression (d = 0.43 [0.18, 0.68]), and anger rumination (d = 0.41 [0.18, 0.63]). MEA + CR was particularly effective in reducing anger expression (d = 0.66 [0.21, 1.11]), aggression (d = 0.90 [0.42, 1.39]), and anger rumination (d = 0.80 [0.40, 1.20]) for individuals who reported high values (+1SD) of the outcomes at baseline. Conclusions: Brief therapist-supported internet-delivered MEA and CR treatments are effective interventions for maladaptive anger. Combining MEA and CR is especially effective in reducing anger expression and aggression, particularly, in individuals who report higher levels of initial anger pathology. The present study highlights the importance of emotion regulation as an important treatment target for reducing maladaptive anger.