A simple isocratic and rapid reverse phase high performance liquid chromatographic (RP-HPLC) method was developed and successively validated stability for the estimation of Sitagliptin and Metformin HCL. Sitagliptin and Metformin HCL were resolved on an isocratic method, C8 Column, mobile phase utilizing a composition of 2.34g of Sodium 1-Octane Sulfonate Monohydrate : Acetonitrile(67:33 v/v pH 3.0) at a flow rate of 1.0 mL/min with UV detection at 210 nm. Retention Time of Sitagliptin and Metformin HCL were 13 min and 3.5 min respectively. RP-HPLC method for determination as well as force degradation study of Sitagliptin and Metformin HCl was Validated.The results of specific ,precise, accurate, linear, robust, rugged were proved within the limits as per ICH guidelines. The method could be used to select the storage condition improving the manufacturing process and for routine analysis of Sitagliptin and Metformin HCL in their combined dosage forms.