A three-dimensional numerical model for laser surface transformation hardening of metals using the finite differential technique is given in this peper. The model takes into account the finite dimensions of the workpiece, the temperature dependence of thermalPhysical properties of the material, the laser processing parameters, and the surface heat losses due to convection and radiation. According to the model a three- dimensional temperature distribution on the surface and inside the workpiece can be obtained. The model can also be used to predict the phase transformation depth resulting from the laser surface treatment. Good agreement is demonstrated with experimental results for laser hardening of a zirconium alloy.