This research aims to: 1) develop a hypothetical model of conflict management in form of a module to be used as a guideline in conflict management assessment and treatment, 2) determine the effectiveness of conflict management in improving the emotional stability of the eleventh graders in senior high school students, in Karanganyar. The research approach applied is “Research and Development”, and the subjects involved were senior high school students (11th Graders) in Karanganyar who had low emotional stability. However, based on the results of the inventory scores distributed to students, among 292 students and there were 40 who had low emotional stability. The result of the inventory also functioned as a pre-test, and the research subjects were treated with conflict management technique, organized in the conflict management module, which were given in four sessions. After the treatment research subjects were given the same inventory pre-test, which served as a post-test, and analyzed with a proper module rational test and a t-test. The research designed one group pretest-posttest in order to determine the effectiveness of conflict management in improving emotional stability. Results have shown that conflict management module has proved to be effective; based on the subject matter experts, practitioners, and students, producing a percentage of 98.8% viability by experts and practitioners, and 84.25% by the students. Besides, to test the effectiveness of the t-test (t = 9672) the results obtained with the significance of 0000, compared with the table t (df = 39, sig 5%, t = 1.68488), then t count > t table, which proved to be significant. Thus, there are significant differences between pre-test emotional stability and post-test emotional stability with an improvement of 20.68%.