A stability indicating reverse phase High performance liquid chromatography (RP-HPLC) method has been developed and subsequently validated for the simultaneous determination of Atazanavir and Cobicistat in bulk and pharmaceutical formulation. Separation was achieved in isocratic mode with a Kinetex C18 100 A (250 mm x 4.6 mm,  5µ) column and mixture consisting of 0.1% OPA(pH 3) and methanol in 80:20 v/v was used as mobile phase with a flow rate of 1 ml/min, column temperature at 25°C and the run time as 10 mins. UV detection was performed at 239 nm and the sample temperature was maintained ambient. The described method for simultaneous determination of Atazanavir and Cobicistat is linear over a range of 8 μg/ml to 120 μg/ml and 5 μg/ml to 60 μg/ml respectively. The method shows good precision results which were below 2.0%RSD. Limit of Detection (LOD) and Limit of Quantification (LOQ) of Atazanavir and Cobicistat was established and found to be 1.49 and 4.97 μg/ml and 1.13 and 3.77 μg/ ml respectively. The developed method was validated according to ICH guidelines for various parameters.The method is simple, rapid, selective and stability indicating method which would be used for regular stability indicating quality control determinations.