To achieve sustained release of local anesthetics from injectable formulations, polycarbonate microspheres were prepared by a solvent-evaporation process. Release patterns of benzocaine, lidocaine, and dibucaine from polycarbonate microspheres in vitro were investigated. Drug contents and sizes of microspheres affected the release patterns of the local anesthetics. The release rate of drugs from smaller microspheres was greater than that from larger microspheres, and with increase in the drug contents, the release rate increased. Microspheres before and after release studies were observed by scanning electron microscopy. It was confirmed that the use of polycarbonate microspheres resulted in sustained release of local anesthetics.