Large-scale NiS2 minicrystals with size of 5-10 mu m were synthesized by ultrasonic spray pyrolysis technique. The shape of the obtained NiS2 minicrystals ranges from tetrahedron to cone. It was found that these two shape formations of tetrahedral and conical NiS2 minicrystals were temperature-dependent, i.e., with temperature increasing, such as high to 743 K. it would result in the formation changing from tetrahedron to cone. It indicates that the nucleation probability of tetrahedral structure is larger than that of conical structure. The nucleation thermodynamics and growth mechanism were proposed to elucidate the temperature-dependent shape evolution. The theoretical predications are in good agreement with experimental results, suggesting that the thermodynamic driving force and the Gibbs free energy difference between two phases are the physical origin of the shape evolution. (C) 2010 Elsevier B.V. All rights reserved.