Phase transition of gamma-Al2O3 was studied under hot isostatic pressure (HIP), using a SUS304 capsule. The transition of gamma- to alpha-phase was accelerated by the pressure. In order to complete the transition, it is necessary to heat gamma-Al2O3 at high temperature of 1300 degreesC for a long time. However, applying 200 MPa, gamma-Al2O3 transformed into alpha-Al2O3 even at 500 degreesC. The transition temperature increased with the decrease of HIPing pressure. Typical "S" curves were obtained in the kinetic relation between the conversion and time. Avrami plots of the conversion and time revealed that the phase transition proceeded by nucleation process. Hence, the nucleation seems to be induced by the stress at the contact points of powder particles, which is applied by the Wing pressure through the capsule. On the other hand, particle size was largely increased by the transition. A small amount of water contained in the gamma-Al2O3 was also considered to play a role of hydrothermal medium for the transition. Therefore, it is deduced that the HIPing pressure induces the nucleation and that a small amount of water in gamma-Al2O3 accelerates the transport at low temperature. (C) 2004 Elsevier B.V. All rights reserved.