a new microsphere formulation for controlled - or sustained - release delivery of therapeutic ingredient , mainly peptides and proteins not over 10k in molecular weight , comprises at least a therapeutic ingredient , a helping agent and a biodegradable polymer . the therapeutic ingredient and the helping agent are in the form of fine particles , less than 1o um in diameter , encapsulated in the polymer which forms the microsphere matrix . a method for preparing the composition comprises a step of in - situ precipitating the therapeutic ingredient and the helping agent to the fine particles and successive steps for forming the microspheres . such a microsphere formulation offers a well - controlled release profile for prolonged period and encapsulation efficiency over 95 %.