Conventional alginate bead has been limited to be used as a drug carrier because of its large size. To overcome the disadvantages of conventional large-size alginate drug beads, Ca-alginate microparticles were prepared using membrane emulsification method controlled with the sodium alginate concentration and the pressure of reactor. The optimal monodispersed microparticles were obtained with the concentration of 2 wt% alginate solution and the pressure of 0.4×10⁵ Pa. The mean size of our prepared microparticles was about 4 ㎛. As the drug solutions, lidocaine·HCl(cationic), sodium salicylate(anionic) and 4-acetamidophenol(nonionic) were selected. These three different drugs were loaded in the drug carrier of prepared alginate microparticles. Drug releases were performed in the siduim phosphate buffers of pH 2 and pH 7 and ionic strength of 0.2. The release behavior with the variation of drug charge showed that of the cationic drug release was retarded more than anionic one due to the ionic interaction between carboxyl group of alginates and positive charge of cationic drug. From the comparison experiments of the buffers of pH 2 and pH 7, the release was much retarded at pH 2 buffer due to ionic repulsivw force or ionic attractive force between the carboxyl group and the hydroxy or sodium ion in the buffer. Conclusively, the usage of small-size pH sensitive microparticles as a drug carrier has a high potential for the application of drug delivery systems.