Abstract: The effect of cellulose ether substitution ,particle size and viscosity of hydroxy-propylmethylcellulose(HPMC )on the dissolution from hy drophilic matrix tablets was studied withcaptopril(I),chlorpheniramine maleate(II)and indomethacin(III)as model drugs. It was foundthat the dissolution of drugs from matrix was connected with the physico-chemical properties of HPMCand drug solubility.The dissolution of I and II matrix tablets was slower with higher hydroxypropylcontent,but for III the result was the opposite,Hence ,hydroxypropyl content was the major factoraffecting the dissolution. The range of HPMC particle size from below 60 mesh to above l20 meshgave similar release rate for l and II ,but smaller particle size would give slower dissolution rate fromIII matrix. HPMC K100 gave the highest dissolution rate for all three drugs, which were released innearly 60 min. Variation in viscosity of HPMC K4M,K15M and K100M showed insignificant differ-ence in dissolution rate for I and II, and higher viscosity of HPMC gave slower release for III matrix tablets.