Sustained release of macromolecular drugs from polymeric matrices has received increasing attention in recent years. Vaccines that are required to be given in multiple divided doses are not efficacious if only one dose is given without boosting. In order to be effective, most vaccines require two or three booster doses after primary immunization. Therefore, the conversion of multiple dose vaccines into single dose vaccines may represent an important advance. Among the various tentative for improving the administration of proteins, the microencapsulation into biodegradable polymers represents a practical and promising approachControlled drug delivery technology using biodegradable polymers as carriers represents one of the most rapidly advancing area of science.