Background: Innovative methods for smoking prevention interventions need to be investigated to increase attractiveness, access hard-to-reach populations, and increase effectiveness. We studied the feasibility and immediate effects of an intervention to reinforce norms and behaviors of young people related to antismoking, integrated into a popular online community game. Methods: A pilot randomized controlled trial was conducted through the HABBO online community. The intervention group was exposed to repeated discussion sessions with small groups of peer players and two facilitators once a week for 1 month (four sessions), inside the game. The control group had access to antismoking information websites. Process indicators (attractiveness, participation) and immediate outcomes (norms and intentions with regard to smoking) were assessed by questionnaire. Results: One hundred sixteen players were invited to participate in the intervention; 10 did not meet eligibility criteria, 30 were allocated to the intervention group, and 76 to the control group. Median age was 23. Twenty-four percent were not in education, employment, or training. A median of eight players attended each session and the median number of exchange chats by session was 399; 70% of chat time was occupied by the players. Twenty players attended all four sessions. Immediate norms, representations, and intentions were evaluated in 39 players and showed small differences between groups. Conclusion: Delivering and evaluating a smoking prevention intervention in an online game is feasible. In the targeted online community game, the intervention was attractive and allowed the delivery of innovative interventions to audiences with diverse social profiles. Long-term effects, sustainability, and evaluation methodology are discussed.