This study examines inducing an additional phase transformation subsystem using alpha-Al2O3 seeding techniques in a theta-Al2O3 powder system that undergoes theta- to alpha-phase transformation. It is found that seeding induced subsystem occurs independently at temperatures lower than that of the parent (original) theta-powder system. The whole system is composed of two parallel and subsequently occurring phase transformation systems during the heat treatment: the seeding-induced subsystem and the residual parent system. The fraction of the seeding induced subsystem in the whole system increases and eventually can become predominant with greater amounts of alpha-Al2O3 added. The subsystem achieves faster growth of theta-crystallites up to the critical size (d(c0)) of phase transformation and can begin the transformation at a lower temperature. Thus as the seeding-induced subsystem becomes predominant, the phase transformation behavior of the parent system is gradually obscured and is finally replaced by that of the subsystem, with an apparent reduction in transformation temperature of the overall system. The seeding affected subsystem exhibited lower activation energy in nucleation stage of the phase transformation. However, the activation energy of the growth stage for both seeded and unseeded systems may have similar values. (C) 2002 Elsevier Science B.V. All rights reserved.