While the commercial benefits of high pressure processing (HPP) on pulp products (e.g. guacamole) are known, little information is available on HPP of whole avocado tissue. We examined HPP effects on the quality, physiology, biochemistry and microstructure of avocado slices. Flesh colour was affected, with L (lightness) and C (chroma) values decreasing after some treatments, although these changes were not obvious visually. HPP (> 300 MPa) dramatically reduced respiration rates and ethylene production 1 h after treatment, and particularly after 17 h at 20 °C. Treatment resulted in some peroxidase (POD) activity reduction, particularly at higher pressures, while polyphenoloxidase (PPO) activity was generally increased. HPP (600 MPa) induced changes in the cell wall structure, disruption of the cellular network and coalescence of oil vesicles. HPP treatment of avocado slices provides potentially beneficial reduced respiratory activity, without obvious colour changes — a solid foundation for examining shelf life quality implications.