Objective: To investigate the effect of genistein on proinflammatory cytokines, NF-κB activation, and estrogen receptor-β expression in a mice model of endometriosis. Methods:Forty female mice (Mus musculus) were divided into eight groups (n=5 each), including the control (untreated) group, endometriosis group, and the endometriosis groups were given various doses of genistein (at doses of 50; 100; 200; 300; 400; 500 mg/day). Analysis of TNF-α, IL-1β, IL-6, and IL-8 level were done by ELISA technically. Analysis of estrogen receptor-β and NF-κB were done by immunohistochemistry. Results: The level of TNF-α, IL-1β, IL-6, and IL-8 were significantly higher in the EM group compared to the untreated control group (P<0.05). All doses genistein significantly prevented EM-induced increase in TNF-α level (P<0.05), but only at dose of 300 mg/day reach the level in the control group (P>0.05). These increased levels of IL-1β,IL-6, adn IL-8 in the EM group were significantly reduced by all doses of genistein. There were significantly (P<0.05) increased estrogen receptor-β expression and NF-κB activation in EM group compared to untreated group. Only first and fourth dose significantly (P<0.05) decreased the estrogen receptor-β expression compared to the EM group, to reach a level in the control group (P>0.05). All doses genistein significantly prevented EM-induced increase in NF-κB activation (P<0.05), to reach the expression on control group. Conclusion: In conclusion, genistein prohibits the increase in proinflammatory cytokines, NF-κB, and estrogen receptor-β expression in a mice model of endometriosis.