In the recent year, impurity profiling in any active pharmaceutical ingredient (APIs) has become a paramount criterion in pharmaceutical analysis and quality control, espoused by major regulatory authorities like the United States Food and Drug administration (US FDA) CDSCO. Sitagliptin phosphate (monohydrate), a newer dipeptidyl peptidase–4 (DPP–4) inhibitor, an oral hypoglycemic (anti–diabetic) drug intended to be used in type–II diabetes. In the present study an  effort has been made to analyze the related substances present in the Sitagliptin API and was spiked. The study was performed by using High Performance Liquid Chromatography (HPLC) with predetermined chromatography conditions. Two impurities namely Ketoamide and Enamine in various batches procured and were analyzed. The method was validated by using Waters HPLC, Model no. Alliance 2695, with 2998 PDA detector, powered by. Empower– 2 software. The acceptance criteria for resolution was kept between Ketoamide and Enamine impurity from system suitability solution was not less than 2.0, tailing factor  was not more than 2.0. And relative standard deviation for three replicate injections of reference solution was less than 1.0%. The difference between the results of each specified and unspecified impurities from the six different preparations of test solution injections is ± 0.02 and for the total impurities ± 0.05. The average result of Ketoamide and Enamine impurity was found not more than 0.15%.