The objective of the study was to develop smotically driven oral drug delivery system of Aceclofenac, to be taken twice daily. It is also objective of present study to evaluate developed osmotic pump. Sodium chloride & sodium bicarbonate were used as an osmogent. The tablets were coated with cellulose acetate as the semipermeable membrane containing castor oil as a plasticizer and microporous membrane was developed by using polyethylene glycol as a plasticizer and pore forming agent.The emipermiable membrane formed by using cellulose acetate as a polymer and castor oil as a plasticizer, allows the passage of water and is selective in nature, which is essential for the zero-order release of drug.The membrane formed by using polyethylene glycol as a plasticizer cannot act as a semipermiable while it behaves as a microporous membrane, which cannot deliver drug not at zero-order.· The release rate of drug from microporous membrane is at higher rate than as comparative to semipermiable membrane. It can be conclude from the present study and the results obtained that the osmotic pump for release of Aceclofenac can be developed as a twice a day dosage form.( B.D.) Zero-order release rat