The effect of high hydrostatic pressure on the natural microorganisms in cucumber juice was studied.Inactivation of bacteria and the mold & yeast at 300 MPa ,350 MPa, 400 MPa and 500 MPa for 0-15 min treatments were investigated, respectively.The bactericidal effect of high hydrostatic pressure was enhanced with increasing pressure and treated time.The inactivation curves showed sigmoid shapes with three phases of the lag phase, exponential death phase, and stationary phase,and were modeled by the modified Gompertz equation and the modified Logistic equation.The results show that the modified Gompertz equation was superior to the modified Logistic equation.