A new, simple, accurate, precise and reproducible RP-HPLC method for the simultaneous estimation of Sitagliptin Phosphate Monohydrate and Simvastatin has been developed and validated. Chromatographic separation was achieved using Neosphere C-18 column (4.6 mm 250mm,5mm) in gradient mode with a mobile phase consisting a mixture of acetonitrile:methanol:0.1% orthophosphoric acid in water (70:15:15v/v) at a flow rate of 1ml/min. The eluents were detected at 254 nm using UV detector. The retention time of Sitagliptin Phosphate Monohydrate and Simvastatin were found to be 2.09min and 7.79min respectively. The method was linear over the concentration range of 25-150μg/mL for Sitagliptin Phosphate Monohydrate and 10-60μg/mL for Simvastatin. The % recoveries for Sitagliptin Phosphate Monohydrate and Simvastatin were found to be 98.98-101.06% and 99.89-102.43% respectively. The developed method was validated for parameters like system suitability, specificity, linearity, accuracy, precision, ruggedness and robustness as per International Conference on Harmonization guidelines and the results were found to be within the limits. This validated method can be used for the routine quality control analysis of Sitagliptin Phosphate Monohydrate and Simvastatin in combined dosage form.