A major challenge in laser fusion cutting of thick-section ceramics is to overcome the thermal-stress induced cracking, which leads to catastrophic breakdown of the material integrity. In order to achieve crack-free cutting of ceramics, it is important to understand the mechanism of the transient temperature field and resulting stress distribution effect on crack formation. In this paper, both experimental and theoretical investigations are reported to understand crack formation characteristics in fibre laser cutting of thick-section Al2O3 ceramics. A three-dimensional (3D) finite element (FE) model for simulation of the transient temperature field and thermal-stress distribution together with material removal in laser cutting was developed. Crack formation characteristics were predicted by the model and validated by experiments. The effects of four process parameters i.e. laser peak power, pulse duration, pulse repetition rate and feed rate on temperature field, resulting stress distribution and potential crack formation were also investigated in this work. The study indicates that a transition from compressive to tensile stresses can be resulted in as the laser cutting parameters change, which is beneficial to resist the crack formation. Based on the experimental and numerical investigations, the process parameters were optimised and the fibre laser crack-free cutting of 6-mm-thick alumina was demonstrated for the first time. (C) 2011 Elsevier Ltd. All rights reserved.