A bioabsorbable release-sustaining pharmaceutical formulation using a biodegradable release-sustaining base material which can prevent an effective component drug from being released too rapidly just after administration of the formulation and then allow continued release of the drug for at least one month at a defined rate, is provided. For the biodegradable release-sustaining base material, a lactic acid-glycolic acid copolymer (PLGA) with an adjusted distribution in molecular weight is used.