Sexually transgressive behaviour (STB) causes serious problems for, among others, students of higher education. The persuasive card game TALK THAT TALK was designed to promote ethical bystander behaviour in STB situa-tions and contribute to a social transition to less sexual violence. To this aim, the game facilitates Intergroup Dialogues between female and male players. A con-trolled experiment was conducted to evaluate the game. The outcome variables of the experiment were obtained from the literature: Willingness to Intervene, Awareness of prevalence of STB, and Bystander Responsibility. Quantitative and qualitative analyses, including validated questionnaires and semi-structured in-terviews, were employed to measure the game’s effects. Participants evaluated the quality of the game (session) and game experience positively and reported that meaningful intergroup dialogues about STB situations took place during the game session. As a result, in the experimental group a significant increase of the three outcome variables was observed, whereas in the control group a non-sig-nificant decrease was found. However, due to a selection bias in the recruitment of participants the effects were possibly overestimated. Reversely, a lack of prac-tical skills training in the game may have led to an underestimation of the effects. We concluded that the game TALK THAT TALK may promote ethical bystander behaviour in STB situations by facilitating an intergroup dialogue between fe-male and male participants. Future research should establish if the results can be generalised to a more representative sample of participants and if the game ef-fects may be improved when institutes for higher education include the game in large-scale intervention programmes against sexually transgressive behaviour.