An HPLC assay method for determining of lovastatin in the presence of its degradation products was validated under acidic, basic, hydrogen peroxide, high temperature, and photoirradiated conditions. The HPLC system consisted of a Lichrospher 100 RP-18 (5µm) column, and a guard column of Lichro CART (150x 3.9) using a mobile phase of acetonitrile-phosphoric acid(0.1%) (50:50,v/v) with UV detection at 238 nm. The results indicate that the established assay method is suitable for stability measurements of lovastatin. From the stress treatments, lovastatin was determined to be sensitive to the light, acidic, and basic medium.