Provided is a method for preparation of a sustained released pharmaceutical composition, wherein an active ingredient and a cellulose derivative dissolved in a lower alkyl alcohol solvent are processed with granulation such that the PEO does not need to be processed with granulation or sizing to achieve uniform drug distribution. Besides, the specific range of the viscosity of the cellulose derivate provides better uniformity to the sustained release pharmaceutical composition derived from the above preparation method.本發明提供一種緩釋性醫藥組合物之製備方法,其藉由先將藥物與纖維素衍生物以低烷基醇溶劑進行造粒,進而使氧化烯聚合物無須歷經造粒或整粒,即可達到較佳均一度之效果。此外,本發明藉由特定黏度範圍之纖維素衍生物,使前述製備方法所得之緩釋性醫藥組合物中具有較佳均一度之優點。