A novel, simple, specific, accurate, precise method development and validated for the simultaneous estimation of Losartan and Hydrochlorothiazide by RP-HPLC in bulk and marketed formulation. A High Performance Liquid Chromatography WATERS Alliance 2695 separation module, Software: Empower 2, 996 PDA Detector with Altima C18 (4.6×150mm, 5.0 µm) column, with mobile phase composition of Methanol and TEA Buffer pH 4.5: Acetonitrile taken in the ratio of 50:25:25% v/v/v was used. The flow rate of 1.0 ml min-1 and effluent was detected at 225 nm. The retention times of Losartan and Hydrochlorothiazide was 2.102 and 3.537minutes. Linearity was observed over concentration range of 5-25µg/ml and 12.5µg/ml for Losartan and Hydrochlorothiazide respectively. The Limit of detection and limit of quantification of Losartan and Hydrochlorothiazide was found to be 0.2ng ml-1 and 2.3ngml-1 & 0.8ng ml-1 and 7.04ngml-1 respectively. The accuracy of the proposed method was determined by recovery studies and found to be 98% to 102%. Then method was validated in terms of linearity, accuracy, precision, (repeatability, intermediate precision) specificity (by assay), robustness and system suitability. Thus, the validated method is can be successfully applied to routine analysis for regulate the quality. It also should be used for analytical research purpose.