The main objective of the proposed study is to develop and validate a new stability indicating reverse phase HPLC gradient method for the simultaneous estimation of olmesartan medoxomil and chlorthalidone in combined dosage form. The method is optimized by using zorbax phenyl column (250 x 4.6 mm, 5 μ). For pump-A, ammonium dihydrogen orthophosphate and pump-B, acetonitrile: are used. Phosphate buffer pH was adjusted with orthophosphoric acid to 3.0. Water and acetonitrile (45:50) are used as diluent. The flow rate is 1.5 ml/min and the elutant is monitored at 220 nm with uv detector. The retention time of olmesatran medoxomil and chlorthalidone are 10.70 ±0.1 mins and 4.8 ± 0.1 mins respectively. Precision shows that % Relative standard deviation of olmesartan medoxomil and chlorthalidone is about 0.23 and 0.56 respectively. The percentage recoveries of both the drugs olmesartan medoxomil and chlorthalidone from the dosage formulation are 100.3% and 99.20% respectively. Linearity of olmesartan medoxomil and chlorthalidone is in the range of 10.0 to 60.0 μg/ml and 6.25 μg/ml respectively. Calibration curve shows good linearity and range. The correlation coefficient of olmesartan medoxomil and chlorthalidone is 0.999. And the results obtained for Robustness and Ruggedness are well within the acceptance criteria. The proposed method is found to be simple, rapid, accurate and precise. It is found to be economical and suitable for simultaneous determination of olmesartan medoxomil and chlorthalidone in pharmaceutical dosage form.