The influence of high pressure carbon dioxide (HPCD) on the activity and structure of pectin methylesterase (PME) from orange was investigated.The pressures were 8-30 MPa,temperature 55 ℃ and time 10 min.HPCD caused significant inactivation on PME,the lowest residual activity was about 9.3% at 30 MPa.The SDS-PAGE electrophoretic behavior of HPCD-treated PME was not altered,while changes in the secondary and tertiary structures were found.