The present paper describes the development of a reverse phase chromatographic (RPLC) method for montelukast sodium in the presence of its impurities and degradation products generated from forced degradation studies. The drug substance was subjected to stress conditions of hydrolysis, oxidation, photolysis and thermal degradation. The degradation of montelukast sodium was observed under acid and oxidative environment. The drug was found to be stable in other stress conditions studied. Successful separation of the drug from the process impurities and degradation products formed under stress conditions were achieved on an Atlantis dC18 (250 x 4.6 mm) 5 μm column. The gradient LC method employs solution A and solution B as mobile phase. The solution A contains aqueous 0.1% OPA and solution B contains a mixture of water, acetonitrile (5:95 v/v). The HPLC method was developed and validated with respect to linearity, accuracy, precision, specificity and ruggedness.