Introduction: Anti-cancerous effects of cyclooxygenase-2 (COX-2) inhibitors have been reported in different cancers. High expression of COX-2 has been demonstrated in various neoplasms such as colorectal, gastric, esophageal, breast, non-small cell lung cancers, and pre-neoplastic lesions such as colorectal adenomas and Barrett's esophagus. Goal: The purpose of this study was to investigate percentage of positive COX-2 expression in skin tumors, including pre-malignant and malignant tumors. Methods: This is an analytic cross-sectional study that includes 62 skin tumor samples, among which 49 samples were malignant and 13 were pre-malignant. After study for determination of pathologic kind of tumors, samples underwent immunohistochemical study for COX-2 expression. The DakoCytomation EnVision+System-HRP is a two-step extremely sensitive IHC staining technique