The effects of temperature and pressure on the size-dependent solid phase transition of the In2O3 nanocrystals have been theoretically investigated on the basis of a simple thermodynamic model. It is demonstrated that the transition pressure and temperature changes are dominated by surface energy and surface stress. The high temperature and high pressure conditions favor the nucleation and growth of the rhombohedral phase. The model predictions are supported by recent experimental results. (C) 2013 Elsevier B. V. All rights reserved.