To clarify the process that preschoolers' prosocial behavior occurs, with the existence of troubled people, a naturalistic observation was conducted on 47 preschool children for a period of 45 (15minutes x 3) minutes. Children were observed and the records show in some episodes where the existance of troubled people caused a drastic change in the children's prosocial behavior. In those episodes, the categorized prosocial behavior was analyzed in a series of order to show the process that preschooler's prosocial behavior occurs. Also, it was analyzed whether the categorized prosocial behaviors were effective. The results show that the preschoolers tried to solve the situation by combining some, though limited, strategies. However, the results also show that spontaneous prosocial behavior did not work as effective as the one occured on request by troubled people or teachers and spontaneous expression of prosociability towards troubled people was difficult for the preschoolers. Some were also not very effective in practicing prosocial behavior, although they tried to help the troubled people by combining a variety of different strategies. It remains as a future issue as to how we provide educational support to those preschoolers.