Abstract: Endometriosis is a common, complex and chronic disease related to ectopic implantation and growth of endometrial tissue. Endometriosis is characterized by the presence and/or the growth of endometrial tissue (both glands and stroma) outside the uterine cavity that causes inflammation inside or outside the pelvis. This study aimed to investigate the possible role of COX-2 in endometriosis and its relationship with leptin, lipid peroxidation, nitric oxide and TNF-α. Materials and methods: Endometriosis was surgically induced in 16 female albino rats. Animals were divided into three groups. Group 1 (normal control group) was given only the solvent (PEG:saline) of celecoxib. Group 2 (endometriosis induced) was given PEG:saline Group 3 treated endometriosis with celecoxib. Results: endometriosis group showed significant increase in serum levels of leptin, lipid peroxidation (MDA), nitric oxide and highly significant elevation in serum level of TNF-α. Administration of celecoxib in endometriosis showed significant reduction in the serum levels of leptin, lipid peroxidation (MDA), nitric oxide and highly significant decrease in serum level of TNF-α. In conclusion: the current study suggests that selective COX-2 inhibitor celecoxib could ameliorate endometriosis.