osmotic ABSTRACT The Controlled porosity osmotic pump drug delivery system suitable for oral administration typically consists of a compressed membrane that is coated with a semi permeable membrane that has pore-forming water-soluble additives, which after coming in contact with water, dissolve, resulting in an in situ formation of a micro porous structure for drug release. Drug delivery from these systems is not influenced by the different physiological factors within the gut lumen. The main objective of this is to formulate CPOP for controlled release of a Diuretic, Hydrochlorothiazide, which is expected to improve patient compliance due to reduced frequency, it also eliminates the nead for complicated and expensive laser drilling and maintains continuous therapeutic concentration. Hydrochlorothiazide belongs to the thiazide class of diuretic. It has variable absorption from GI tract with oral Bioavailability of about 70% and a plasma elimination half life ranging from 5.6 to 14.8 hrs. CPOP formulation of Hydrochlorothiazide were prepared using different concentrations of solubilizing agent as it is belongs to poorly water soluble BCS class II drug and different osmogens at different concentrations by wet granulation technique. The tablets were coated by pan coating with cellulose acetate and PEG -400 as pore forming agent. Prepared tablets were evaluated for tablet thickness, hardness, weight variation and drug content analysis, drug release studies. As the osmogen concentration increases the rate of drug release was found to be increased and optimum concentration of osmogen was found to be 1:6. And it follows zero order release kinetics.