Abstract: Objective To evaluate the expression level of oxytocin receptor (OTR) in smooth muscle of myometrium and its correlation with the degree of dysmenorrhea in adenomyosis. Methods Fifty AM cases and 20 uterine myoma cases admitted to department of gynecology in our hospital from September 2013 to August 2014 were enrolled in this study. Immunohistochemical S-P method was used to identify the expression of oxytocin receptor in smooth muscle of myometrium from 20 cases with pathologically confirmed normal myometrium and 50 female patients with pathologically confirmed adenomyosis. The expression level was detected by using digital image analysis with optical microscope and Image Pro-Plus 6.0. Results The positive expression rates of OTR in smooth muscle of myometrium in AM group were higher than that in controls (62 370±34 758 vs 16 082±11 125, P< 0.01), and the expression level increased with the aggravation of dysmenorrhea. All the differences were statistically significant. Conclusion The expression level of OTR in smooth muscle of myometrium is positively correlated with the degree of dysmenorrhea. This indicates that the increased intensity of uterine contraction is involved in the pathogenesis of dysmenorrhea.