Considering the effect of the electrostatic energy on the phase stability of binary alloying nanoparticles, we proposed a charge-dependent thermodynamic model to address the phase transformation between miscible and immiscible when the size of alloying particles goes into the nanometer scale. We found that the miscible system would transform into immiscible when the size of alloying nanoparticles reduces to a critical size. Surprisingly, the system would return miscible from immiscible again when the size further reduces to less than the critical size. The physical and chemical origin of the anomalous transition between miscible and immiscible was pursued. (c) 2006 Elsevier B.V. All rights reserved.