This study examined the social problem solving of the interpersonal conflict situations in preschool children. Children's strategies in free-play session were observed and analysed to examine whether the strategies adopted for resolving conflicts would be different when they were in conflict with the same-age members or with the different-age members. The relationships among the children were also varied in terms of children's membership in the same or different play groups. Eighty-seven preschool children of 4, 5 and 6-year-olds (45 boys and 42 girls) were observed in free play situation. Observations were made once a week from May 1993 to December 1993 and videotaped. A total of 140 conflict episodes were collected and analysed. The results indicated that children adopted different strategies for resolving the conflicts according to the group membership of their rivals and that the quality of social problem-solving strategies changed with age from egoistic responses to social responses. It was also found that in the cause interpersonal conflicts and the social problem solving were related to membership of the conflict situations with their peers. Implications of these findings were discussed in terms of the development of social cognition.