Abstract In this study, nattokinase (NK) was microencapsulated in high-molecular-weight Na-γ-PGA, and the amount of NK added to the Na-γ-PGA was in the ratio of 1:1 and 2:1 w/w, which was designated as NK-100 and NK-200, respectively. The temperature and pH stability of microencapsulated NK were found to be higher than those of the free form. Free NK lost its overall initial activity after treatment at a temperature above 60 °C or at a pH less than 5.0 for 1 h. NK-100 and NK-200 retained 35% and 60% of their activities after exposure to an acidic condition of pH 4.0 and possessed 18% and 25% activity after treatment at 60 °C for 1 h, respectively. Furthermore, NK-100 and NK-200 exhibited more protective bioactivity than free NK did in storage stability tests. This simple and versatile approach can be potentially applied to the microencapsulation of various biomolecules for drug-delivery applications.