A model of a primitive cation MZ+ in aqueous solution is introduced in order to clarify the influence of ion charge on hydration structure of cations. A molecular dynamics study for this purpose was performed using a flexible non-constrained model of water molecules. It is shown that the increase of cation charge stabilized an octahedral arrangement of cation and significantly modified the intramolecular geometry of water molecules in hydration shell. For highly charged cations M4+ and M5+ the effect of deprotonation of some water molecules in hydration shell was observed. This phenomenon was treated as a cation hydrolysis. For correct description of this phenomenon the considered model was improved by introducing the effects of charge redistribution between hydrolysis products, which essentially modified and stabilized the hydrated-hydrolyzed structure of cation. (C) 2005 Elsevier B.V. All rights reserved.