A sustained release composition comprising a polymer and manufacturing method thereof. The sustained release composition comprises a polymer, a bioactive agent, and a release rate determined agent, wherein the release rate determined agent is dispersed in the sustained release composition to control the release rate of the bioactive agent. The method comprises providing an oil phase comprising a bioactive agent, a polymer, and a release rate determined agent； providing an aqueous phase comprising a surfactant； mixing the oil phase with the aqueous phase to form the sustained release composition having a controlled release effect.
