Three dimensional objects are built without the use of molds with a new technology called stereolithography. The objects are obtained in an additive way polymerizing under a laser beam a low viscosity liquid resin section by section. The kinetic behaviour of the resin represents a key point For a full comprehension of the cure condition occurring in the small zone exposed to laser irradiation. In this work. the isothermal kinetic behaviour of a commercial acrylic resin for stereolithography is analyzed by differential photocalorimetric analysis. A kinetic model. accounting for the effect of autoacceleration. vitrification and light intensity on the reaction kinetics is presented. In particular. the effect of irradiation intensity on the model parameters is studied correlating the kinetic constant and the final chemical conversion with the light intensity and with a characteristic time scale of the reaction.