An ideal drug delivery system should deliver precise amounts of a drug at a preprogrammed rate to achieve a drug level necessary for treatment of the disease. For most drugs that show a clear relationship between concentration and response, the drug concentration will be maintained within the therapeutic range, when the drug is released by zero-order rate. In order to design a controlled release delivery system, many factors such as physicochemical properties of the drug, route of drug administration, and pharmacological & biological effects, pharmaceutical excipients used etc. These excipients are various materials. Now a days for controlled release drug delivery, polymers are used by large. So this area is now focused by researchers in large. Many developments are taking place in this field. An important consideration in designing polymers for any controlled release mechanism is the fate of the polymer after drug release. Polymers that are naturally excreted from the body are desirable for many controlled release applications.