There were two purposes of this study. The first was to search for the possibility of cooperative learning for prosocial behavior in preschooler. The second was to find preparation necessary to cooperative learning. Two discussions concerning the scene of the crying child and the child who held the dislike were performed. There were three common flows (①Production of action, ②Expectation of result, ③Examination of reason and possibility of other methods) in two discussions. It showed that preschooler were to be able to match others' opinions and my opinions, and to be able to learn the best action for an embarrassed person. In addition, result of the interview executed ahead of the cooperative learning showed the necessity of preparation to enable preschooler's cooperative learning. The preparation was training of the idea to the scene of an embarrassed person rather than discussion skill. Therefore, even though it was preschooler, with set up the idea to devise the action for embarrassed person by preparation, the cooperative learning was effective to learn the prosocial behavior.