Abstract: A HPLC method for determination of rofecoxib in human serum was presented. The method is based on pre-column derivatization of analyte to a phenanthrene derivative of drug. Rofecoxib and internal standard were extracted from serum using liquid-liquid extraction. Upon exposure to UV light, drug was found to undergo a phtocyclization reaction giving a species with high absorbance. Validation of the method has been studied in the concentration range of 2-100 ng mL-1.