Study aim: To assess the effect to fone term of stretching exercise on primary dysmenorrheal in high school students. Material and methods: 60 single girls aged 18-22 years with moderate-to-severe primary dysmenorrhea are select from school of physiotherapy, R.K. University. The students are non-athletes and volunteered for the study. The participants are randomly divided into 2 groups: an experimental group (n = 30) and a control group (n = 30). In the intervention group, the subjects are requested to complete an active stretching exercise for 8 weeks (3 days per week, 2 times per day, 10 minutes each time) at home. In the pre-test, all of subjects were examined for pain intensity (10-point scale), pain duration, and the use of sedative tablets in 2 continuous menstruation cycles. The post test was examined 8 weeks later. Results: After 8 weeks, pain intensity is reduced from 7.65 to 4.88, pain duration is decreased from 7.48 to 3.86 hours, and use of sedative tablets is decreased from 1.65 to 0.79 tablets in the experimental group (p<0.05). In the control group, a significant decline is only noted for pain duration(p<0.001). Conclusions: Stretching exercises are effective in reducing pain intensity, pain duration, and the amount of painkillers used by girls with primary dysmenorrhea.