Abstract: A method for producing sustained release microsphere preparation for water-soluble medicament, which has high incorporation efficiency of the medicament and low initial burst, which comprises dissolving water-soluble pharmaceutical active ingredient and water-insoluble biodegradable polymer in one or two solvents in which both can dissolve, removing the solvent to give a solid dispersion having the water-soluble pharmaceutical active ingredient dispersed into said biodegradable polymer at molecular level, and further, dissolving said solid dispersion in an organic solvent being water-immiscible and having a boiling point of below 100.degree. C., and adding the resulting oil phase into an aqueous phase containing emulsifying agent to give O/W emulsion, and followed by removing the organic solvent from the oil phase of the resulting emulsion.