Objective: To examine the effectiveness of Group Triple P (GTP) administered to parents of children with developmental disorders by public health nurses Procedure: Twelve parents of children with developmental disorders were assigned randomly to Group A, which underwent GTP intervention, and to Group B, which underwent no intervention. Group A just after intervention was compared with Group B as the control group by evaluation index. Group A just after intervention was also compared with one month after the intervention and three months after. In addition, the combined Group A and Group B was compared before and after intervention. Results: The control group showed no change, but Group A, which had undergone intervention, showed a tendency toward improvement of the parent's loquaciousness and the child's emotional symptoms. Group A was more significantly improved in depression one month after intervention and in depression, lax child-rearing and excessive response three months after than just before intervention. The combined group was significantly improved in the total scores and excessive response of Parenting Scale (PS), and in the total scores and stress of Strength and Difficulties Questionnaire (SDQ), compared to that just before intervention. Discussion: GTP produced significantly effective improvement in PS, SDQ, stress and depression. Though this study had the limitation of a low number of subjects for examination, GTP was suggested to be an effective support method for the parents of children with developmental disorders.