A reverse phase liquid chromatographic (RP-LC) method was developed for the quantification of the related impurities of Fesoterodine Fumarate drug substance. The method was optimized using buffer (prepared by dissolving 3mL H3PO4 (85%) and 1.0gm 1-Octane sulphonoic acid sodium salt anhydrous taken in 1000mL milli- Q-water and then pH was adjusted to ~ 7.2 with dilute potassium hydroxide solution) taken along with Acetonitrile 60:40v/v as mobilephase-A, and Acetonitrile: water in the ratio of 90:10 v/v as mobile phase-B. The flow rate was set at 1.2 mL min-1, wavelength at 220nm respectively and the column temperature was maintained at 45°C. The capability of stability indicating method developed was demonstrated by studying the degradation products generated during the forced degradation studies under the following conditions i) water hydrolysis, ii) at 75% relative humidity, iii) oxidative, iv) thermal v) photolytic, vi) acid, vii) base, and viii) photolytic degradation. The developed method can be used for the determination of synthetic and degradation impurities in the regular quality control analysis for the drug substance.