This study was to investigate the effects of classroom size on children`s stress behaviors, and to find the relationship between children`s stress behaviors and types of activity 105 kindergarten children were selected and divided into three classrooms according to different classroom sizes: classroom 1(N=28), classroom 2(N=35), classroom 3(N=42). Three early childhood education specialists observed them for four weeks. An analysis of variance, a multivariate analysis of variance and chi-square test were used to analyze the data. The results indicated that 1) the children in classroom 1 showed significantly less passive stress behaviors than children in two other classrooms, 2) the children in classroom 2 and 3 exhibited significantly more active stress behaviors. 3) there was no significant difference in children`s self with self stress behaviors among the children in three classrooms, 4) the different classroom size had a significant effect on self with others stress behaviors and self with objects stress behaviors, 5) there was a significant relationship between types of activity and classroom size, 6) there was a significant relationship between children`s stress behaviors and activity types in the classrooms.