Sustained release of water-soluble captopril (CAP) from microcapsules composed of Ethylcellulose (EC) and Hydroxypropylcellulose (HPC) was studied. The microcapsules were prepared using the emulsion-solvent evaporation technique. Factors affecting the size and size distribution of microcapsules were investigated. The microcapsules were characterized using an x-ray diffractometer, static contact angle instrument and UV/visible spectrophotograph. The microcapsules for the sustained release study had an average diameter of 337 mum, a drug-to-polymer ratio of 1:3 by wt and various polymer compositions. The cumulative releases of CAP from the microcapsules at various times were measured. The results could be well described by a first order release kinetics for first 0.7 h and a zero order release behavior for the release time between 2 and 10 h. The rate coefficients of first and zero-order stages linearly depended upon the polymer composition. The microcapsules rich in HPC showed better sustained-release behaviors. The matrix changed from an anhydrate state to hydrogel may be the cause for the observed release kinetics change.