Observations of children's playground behaviours were obtained in order to explore how they intervened when they saw other children's conflicts. To explore relations among the dominance between peers and intervention which preschoolers showed in the conflict, 6 years-old boys participated in the interview. Results indicated interventions children showed were different from those of teachers'. In additions, in the case study the interventions the target child exhibited were influenced by the dominance between peers, but the interview told the different result in part. The interviews indicated that preschoolers were usually on ""weak"" one's side, but according to circumstances they were influenced by ""strong"" one's dominance.