Abstract: This invention involves the establishment of manufacture of clinically useful controlled release parenteral formulation of buprenorphine hydrochloride/buprenorphine base microparticle delivery system. Buprenorphine and buprenorphine hydrochloride has been used for the treatment of pain and drug addiction. In view of minimizing the frequency of dosing and avoiding surgical procedures, controlled release parenteral dosage forms are developed using biocompatible and biodegradable polymers. These parenteral formulations also avoid oral absorption problems and potential abuse associated with other possible forms of administration such as sublingual, nasal and transdermal dosage forms. Poly-(lactic acid), poly-(glycolic acid) and their copolymers and mixture of these polymers are used for the development of microencapsulation of a buprenorphine and buprenorphine hydrochloride by solvent evaporation from oil/water emulsion.