As the size of liquid water decreases, it freezes to cubic ice (Ic) instead of ordinary hexagonal ice (Ih). This occurrence is thermodynamically considered by determining their size and temperature dependent Gibbs free energies induced by solid-liquid interfacial free energy and solid-liquid interface stress. The obtained results are consistent with the known experimental and theoretical results. In addition, it is found that the melting temperatures of Ic and Ih are similar and the entropy difference of Ih and Ic is negligible. (c) 2006 Elsevier B.V. All rights reserved.