Excipients are materials added along with therapeutic agents; and incompatibility between excipients and therapeutic agents affect the final outcome of the product. Aspirin is an ester and is prone to hydrolysis. This study focus on the effect of magnesium stearate as an excipient on stability of aspirin in granules. For that an accelerated degradation study was done on aspirin-magnesium stearate containing granules. For that, aspirin containing granules were sequentially mixed with increasing concentration of magnesium stearate to develop different test samples and they are type 1 (T1), type 2 (T2), type 3 (T3) and type 4 (T4) granules and heated at 70°c for 2 hours and evaluated the drug content. The drug content of untreated samples was found to be 168mg estimated by UV/Vis spectroscopy. The assay of different granules were for T1- 77.11%, T2- 96.7%, T3- 58.02% and T4- 53.80% respectively. The results show that, in these granules prepared by wet granulation process, the aspirin is degrading in a non-linear manner as the drug content increases and followed by decreasing. Overall, the study shows that magnesium stearate is an incompatible excipient for aspirin, varying in a non-linear manner, in granules as a lubricant.