This research was the quasi-experimental research. The objectives of this study were to build the teaching plans using role play activities for enhancing preschool children,s assertive behavior, and compare their assertive behavior before and after implementation of the teaching plans.
	The sample were 15 preschool children, at the age between 45 years old at Pimporn Nursery in Samutprakarn Province in the first semester of 2009 academic year, The children,s assertive behavior were identified by individuals observation through six activities including movement and rhythm activity, creative activity, enriched experience activity, free activity, educational game activity, and outdoor activity. The experiment took eight weeks. The instruments used eight teaching plans with role play activities and the preschool children,s assertive behavior checklist. The statisticsal devices employed for the data analysis were mean, percentage, standard deviation and t-test dependent.  
	The result of the study was as follows:
	1)  Obtained eight teaching plans with role play activities for enhancing preschool children,s assertive behavior. 
	2) There was a statistically difference of the assertive behavior  mean score of preschool children after and before experimenting by using the teaching plans at .05 level.
