Background and Aim: Dysmenorrhea is one of the most common problems in females. “Theory of Planned Behavior” is one of the important theories that explains the main process of adopting health behaviors. The present study assessed applying “ the Theory of Planned Behavior in relaxation training regarding the  severity and duration of painful dysmenorrhea in Mashhad girl students.

Materials and Methods: In this Semi-experimental study, 160  first year intermediate students of Mashhad city who suffered from dysmenorrhea were assessed.They had been randomly selected from 5 girl high- schools in the 6^th educational district. They were divided into equal groups  “case” and “control”. Intervention was made in four sessions. The requisite  data was gathered by means of  a researcher designed questionnaire before  and 3 months after the education of the students. Finally, the obtained data was fed into SPSS software (v:16) using statistical  tests including   Wilcoxon, Mann-Whitney, Independent T-test, Paired T and X².

Results: After educational intervention, mean level of knowledge, attitude, perceived behavioral control, and willed performance of relaxation techniques significantly increased  in the case group (P<0.05). These changes were not significant in the control group. Besides, no statistically significant difference in subjective norms was observed between the two groups after intervention. Meditation education group was increased significantly (P<0.05).

Conclusion: Education of relaxation base on the Theory of Planned Behavior is effective in reduced pain intensity and its duration.