Prolonged release microcapsules and their production

A method for producing a prolonged release microcapsule having an average diameter of about 0.5 to 400 .mu.m for injection, which comprises preparing a water-in-oil emulsion comprising an inner aqueous layer containing a water-soluble and non-polypeptidic drug, a drug retaining substance therefor selecting from a member of the group consisting of gelatin, albumin, pectin and agar and an oil layer containing a polymer substance of lactic acid-glyucolic acid copolymer or lactic acid polymer, then thickening or solidifying said inner aqueous layer to a viscosity of not lower than about 5000 centipoises and finally admixing the resulting emulsion with a third aqueous layer to give a water/oil/water ternary layer emulsion and then desorbing the solvent in the oil layer.