The purpose of this is to investigate the effects peer helping and group contribution on social interaction. It is generally believed that peer interaction is a critical developmental milestone of development of preschool children, one that has important implications for children`s cognitive, communicative, and overall social development. Important goals of early childhood education have included establishing productive and satisfying peer relationships, because the peer relationships in preschool years are very influential in normal development and future mental health of the children. The following research questions were formulated to address the purpose of this study: (1) Do group contribution and peer helping increase social interaction? (2) Does will the change in social interaction be maintained in a group? A factorial design(2 group contributions x 2 peer helping conditions x 3 treatment phases) with repeated measures on the all factors was employed as the research design. T재 experimental groups (each group consisted of four isolate subjects and remained peer subjects)were selected and randomly assigned to the four different experimental conditions. The findings of this study revealed that: (1) Group contribution did not show any different effect on social interaction. But peer helping had the significant effects on social interaction. And there were interaction effects between the peer helping and treatment phases (B×C). (2) Group contribution and peer helping increased social interaction more at the post and follow-up phase than at the pre-phase.