Biodegradable microcapsules entrapping water soluble materials such as potassium nitrate, bovine serum albumin, and egg yolk proteins are prepared by the solvent evaporation method in a (W/O/W) complex emulsion system. Effects of preparation conditions of a (W/O/W) emulsion on the capsule morphology and the entrapment efficiency of the core materials are investigated. The entrapment efficiency of the core material is improved by decreasing in the volume fraction and the concentration of salt in the inner aqueous phase, by the irradiation of ultrasonic wave to (W/O) emulsion, and by increasing in the concentration of salt in the outer aqueous phase. The entrapment efficiency decreases by releasing of the core material in the course of wall formation of the microcapsules.