The oxidation and hydrolysis of 0.11–0.14 M acetic acid in supercritical water (SCW) have been investigated at temperatures of 773–873 K and a pressure of 25.0 MPa in a flow reactor. CO and CO2 were the main products at oxygen-rich conditions. For hydrolysis experiments, CH4 and CO2 were produced in nearly equal amounts while the yield of CO was negligibly small. A detailed chemical kinetic model was developed by revising the kinetic parameters of key elementary reactions. The model performance was evaluated by comparison to the present data as well as data from literature. The model predicted the kinetic behavior of acetic acid oxidation fairly well, despite of slight underprediction of CO and overprediction of CH4. It also reproduced satisfactorily the species concentrations during acetic acid hydrolysis at high temperatures. Based on the model, kinetic analyses were further conducted to identify important elementary steps and to infer reaction mechanisms.