¹Department of Pharmaceutics Y.B. Chavan College of Pharmacy, Dr. Rafiq Zakaria Campus Rauza bagh Aurangabad-431001, India DOI : 10.12991/mpj.20162040694 The aim of the present study was to design a controlled porosity osmotic pump tablet of atenolol. The controlled porosity osmotic pump tablet 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. The dosage regimen of atenolol is 25-mg tablet 2 to 3 times a day. The plasma half-life ranges from ~6 to 7 hours. Hence, Atenolol was chosen as a model drug with an aim to develop a controlled release system for a period of 12 hours. The effect of different formulation variables, namely, ratio of drug to osmogent and level of pore former on the in vitro release was studied by applying a full 32 factorial design. Cellulose acetate (CA) was used as a semipermeable membrane. It was found that drug release was directly related to the amount of osmogent and level of pore former. In-vivo study was performed in rabbits and various parameters Cmax, tmax, AUC, AUMC and MRT were calculated and compared with that of marketed conventional tablet. The optimized formulation was subjected to stability studies as per International Conference on Harmonization (ICH) guidelines and formulation was stable after a 3 month study. Keywords : Atenolol, Controlled Porosity Osmotic pump tablet, Antihypertensive , In vivo study