High hydrostatic pressure (HHP) was applied to elucidate its effect on the thermostability of selected enzymes. Pressure reduced the thermal inactivation of lactate oxidase (LOx) at 66 °C and 0.1 – 50 MPa, ascorbate oxidase (AsOx) at 53 °C and 0.1 – 50 MPa, and cholesterol oxidase (ClOx) at 67.5 °C and 0.1 – 600 MPa. Pressure increased the rate of thermal inactivation of choline oxidase (ChOx) at 45 °C and 0.1 – 100 MPa. The optimal pressure for LOx and AsOx was between 50 MPa and 100 MPa based on the pressure where 〖ΔV〗^‡ shifts from stabilizing to inactivating. Pressure stabilized up to 600 MPa for ClOx. In contrast, it is a denaturant for ChOx. For glucose oxidase (GOx) at atmospheric pressure, transition temperature (T’) was 69.66 ± 0.45 °C and increased to 76.04 ± 0.15°C at 100 MPa. This positive shift of 6°C in ΔT’ confirms pressure is preventing protein aggregation.