Simulation code on ablations using femto-second lasers has been developed to investigate the ablation threshold of various metal samples. In this code, effects of absorption of laser lights by free electrons, that by vibrations of free electrons as fluids, that by inner shell electrons, effects of thermal reductions from free electrons to lattice ions, ablations by vibration effects and thermal effects are included. The ablation threshold obtained by simulations is in good agreement with that obtained by experiments. In low fluence regime, vibration effects play dominant role. (C) 2002 Elsevier Science B.V All rights reserved.