Abstract : In the present investigation an attempt has been made to increase therapeutic efficacy, reduced frequency of administration and improved patient compliance by developing controlled release matrix tablets of Losartan Potassium. Losartan Potassium was formulated as oral controlled release matrix tablets by using poly(ethylene oxides) { Polyox WSR 303 }.The aim of this study was to investigate the influence of polymer level and type if fillers namely lactose [soluble filler], microcrystalline cellulose and anhydrous dibasic calcium phosphate [insoluble fillers] on the release rate and mechanism of Losartan Potassium from matrix tablets prepared by direct compression process. Higher polymeric content in the matrix decreased the release rate of drug because of increased tortuosity and decreased porosity. At lower polymeric level the rate and extent of drug release was elevated. On the other hand, replacement of lactose with anhydrous dibasic calcium phosphate and microcrystalline cellulose have significantly retarded the release rate of Losartan Potassium.