A new simple, accurate, precise and reproducible Reverse Phase-High Performance Liquid Chromatography  method has been developed for the simultaneous estimation of Sitagliptin and Metformin in bulk and pharmaceutical dosage form using Symmetry C18 column (4.6 x 150mm, 3.5mm, Make: XTerra) in isocratic mode. The mobile phase has been prepared by using Potassium Dihydrogen Phosphate and Acetonitrile in different ratio at different pH. Several trials have been performed and it was found that ratio 0f 65:35 of Potassium Dihydrogen Phosphate and Acetonitrile respectively was shown a good peak at pH 5.8 which has been adjusted by using Sodium Hydroxide. The detection was carried out at 254 nm. The method was linear over the concentration range for Sitagliptin 10-30ppl and for Metformin 100-300ppm. The % recoveries of Sitagliptin and Metformin were found to be 99.1 to 100.6% and 98.8 to 100.7% respectively. The validation of method was carried out utilizing International Conference on Harmonization (ICH) guidelines. The described High Performance Liquid Chromatography method was successfully employed for the analysis of pharmaceutical formulations containing combined dosage form.