Abstract: Objective To study the relationship between primary dysmenorrhea and prostaglandin(PGF_2α )concentration of peripheral blood in students in menstrual period. Methods A total of 241 students in menstrual period randomly selected from 1 155 female middle school students were divided into<48 hours dysmenorrhea group,≥48 hours dysmenorrhea group,<48 hours without dysmenorrhea group,and≥48 hours without dysmenorrhea group.PGF_2α concentrations in their peripheral blood were determined. Results The PGF_2αlevels in the students of<48 hours dysmenorrhea group were significantly higher than those of the other students(P<0.01).There were significant differences in PGF_2α level between ≥48 hours dysmenorrhea group and≥48 hours without dysmenorrhea group(P<0.01)and between the two groups without dysmenorrhea(P<0.01). Conclusion There is a significant relationship between PGF_2α of menstrual period and primary dysmenorrheal,but dysmenorrhea symptoms may closely relate to the concentration of PGF_2α.