In order to investigate the possibility of applying HPP in the production of soybean paste, the 〖JP3〗effects of HPP treatments (100~500 MPa, 1~20 min) and heat treatments (40, 60, 90℃, 1~20 min) on koji PPO activity were studied, which are important in forming the color of final product. The activation or inactivation kinetics of PPO following HPP treatment was also evaluated. Results showed that HPP treatment at low pressure (100~300 MPa) could activate the PPO activity with maximum relative activity of 135% at 200 MPa for 10 min. While at a higher pressure between 350 MPa and 500 MPa, koji PPO can be inactivated significantly; a larger degree of inactivation was obtained at a higher pressure with a longer pressure holding time. Moreover, the degree of inactivation could approach a maximum level with an endless pressure treatment, the maximum inactivation differed with different pressure levels, which could be expressed as 74.0%, 55.4%, 62.8%, 66.5% at 350, 400, 450, 500 MPa, respectively. Kinetic analysis indicated that the patterns of koji PPO activation or inactivation could be expressed in a different way at different pressure levels. The PPO activation pattern following HPP treatment at 100~200 MPa could be described well by a two-step first-order model with coefficient of determination (R2) higher than 0.970. The survival curves with 250~300 MPa HPP treatment followed the fractional conversion model with R2 higher than 0.994. The biphasic model was proved to be suitable to describe the kinetics of koji PPO inactivation treated by HPP between 350 MPa and 500 MPa, with R2 higher than 0.995. The results support the further investigation in shortening the fermentation time and improving the quality of final product of soybean paste by applying HPP.