It is a common observation that many crystals undergo a change in habit from the equilibrium polyhedral shape to another, kinetically favorable one during their growth. By analyzing the structures and rates of advance of [100] and [110] steps on the (001) surface of the Kossel crystal, and taking into account additional channel of incorporation of growth units into kink sites via the edge of the step, we demonstrate that the rate of advance of [100] step may become larger than one of the [110] step due to the effect of the activation energies for the exchange between terrace and steps. The change in habit of two-dimensional island from the shape bounded by [100] steps at equilibrium to one bounded by [110] steps at higher supersaturations is thus explained. (C) 2002 Elsevier Science B.V. All rights reserved.