The objective of this study was to develop and evaluate controlled porosity osmotic pump tablet (CPOP) system to deliver Verapamil HCl inacontrolledmannerupto24 h. The porous osmotic pump contains pore forming water soluble additives in the coating membrane, which after coming in contact with water, dissolve, resulting in an in situ formation of a microporous structure. Mannitol was used as an osmotic agent and cellulose acetate (CA) was used as semipermeable membrane. Polyethylene glycol 400(PEG-400) was employed as a pore forming agent as well as plasticizer for controlling membrane porosity. The influences of drug: osmogent ratio, concentration of PEG-400 and membrane thickness on the release profiles were investigated using 23 full factorial design and optimized batch was investigated in different environmental media and stirring rates. It was found that drug release rate increased with the amount of osmogent due to the increased water uptake, and hence increased driving force for drug release. This could be retarded by the proper concentration of channelling agent and membrane thickness in order to achieve the desired zero order release profile. This system was found to deliver Verapamil HCl at a zero order rate for24 h. The optimized formulations were subjected to stability studies as per ICH guidelines at different temperature and humidity conditions.