Abstract: The spherical alginate-trypsin microcapsules were prepared by the ionotropic gelation method, which formed the microcapsules by adding sodium alginate-trypsin into aqueous solution containing CaCl₂. The infrared analysis shows that the matrix in microspheres is cross-linked by electrostatic attraction existed between Ca²⁺and—COO^- in alginate. The SEM images indicate that "egg-box" structure and holes exist in the microparticles. The experiments were carried out to evaluate the properties of the microparticles such as drug loading rate, encapsulation efficiency rate and in vitro release rate. The results indicate that the in vitro release rate decreases with increasing the sodium alginate concentration, the encapsulation efficiency and the drug loading get the highest point when the mass ratio of sodium alginate to trypsin is 4 and the sodium alginate concentration in water is 4%. As the mass radio of sodium alginate to trypsin increases, the drug loading decreases and the encapsulation efficiency increases at first and then decreases.