The morphology of antimony islands grown on the graphite surfaces from soft-landed clusters is investigated by applying the dynamical Monte Carlo method to a lattice gas model. The graphite surface is treated as a triangular lattice subject to a periodic boundary condition. Each incident antimony cluster just after impinging to the surface is assumed to adsorb with a compact shape and to migrate on the surface as a mobile cluster having a multilayer structure. Stable islands are also assumed to grow by the coalescence of mobile clusters. In simulations, two types of processes to make the island shape compact are introduced in order to reproduce the characteristic morphologies of antimony islands on graphite surfaces: jumping up of atoms from convex positions at the perimeter of islands to higher layers of the islands, jumping down from higher layers to empty sites at concave positions around islands. In addition, the multilayer structure of islands is approximately treated with an effective double layer model in which higher layers except for the base are substituted by a uniform effective layer characterized only with the density. The simulation shows the rather compact growth of islands for small cluster deposition. A tendency to the ramified growth of islands is also obtained in the simulation for larger cluster deposition. These results are similar to the observed morphology of antimony islands on graphite surfaces. (C) 2004 Elsevier B.V. All rights reserved.