This research investigated the effects of a minority member opting for pro-environmental behavior in spite of his or her loss of personal benefits in a situation of social conflict between beneficiaries and a victim. In the experiment, a minority factor (one or no self-sacrificing minority) and a damage factor (serious or no damage to a victim) were controlled in a game simulating sea pollution. Under the serious-damage condition, the rate of pro-environmental behavior was hypothesized to be higher in the one-minority case than in the no-minority case, but the differences between one-minority and no-minority case would become smaller under the no-damage condition. The results supported this assumption. A self-sacrificing minority was less influential under the no-damage condition. Moreover, the path-analyses suggested that a minority would affect the evaluation of cost and social desirability of pro-environmental behavior.