Objective: The aim of this study was to evaluate the association between -1195 A/G polymorphism in cyclooxygenase -2 (COX-2) gene and the risk of pain occurrence in women with endometriosis (EM). Materials and Methods: -1195 A/G polymorphism in the promoter region of COX-2 gene was analyzed in 32 EM patients with pain, 28 EM patients without pain, and 29 healthy controls in a Chinese population using a PCR-RFLP assay. Results: AA homozygote carriers and A allelic frequencies for -1195 A/G polymorphism in COX-2 gene were significantly increased in EM patients compared with the healthy controls (p < 0.001). In addition, further subgroup analysis revealed that the AA genotype and A allele of the -1195 A/G variant were present at a significantly higher frequency in the severe pain group than those in the mild and moderate pain groups. Compared with the controls, the risk of developing EM was 2.86-fold higher in individuals with -1195 AA containing the haplotype, and the risk of developing pain was 2.33-fold higher in EM patients with -1195 AA containing the haplotype. Conclusions: These findings suggest that the -1195 A/G on the promoter region of COX-2 gene may increase the risk of pain occurrence in EM women, possibly by affecting the rate of gene expression, especially in patients with the pain phenotype.