Temperature affects the polymerization behavior of dimethacrylate-based materials. This study describes the influence of pre-polymerization temperature and exposure duration on polymerization kinetics of a commercial dental photo-activated composite at the top and at 2-mm depth. We used the temperature-controlled stage of a diamond-attenuated-total-reflectance unit to pre-set composite temperature between 3° and 60°C. Composite was light-exposed by a conventional quartz-tungsten-halogen curing unit for 5, 10, 20, or 40 sec. Real-time conversion, maximum conversion rate ( R _p ^max), time to achieve R _p ^max, and conversion at R _p ^max were calculated from infrared spectra. Composite pre-warming enhanced maximal polymerization rate and overall monomer conversion (top significantly greater than 2 mm). Time when R _p ^max occurred did not change with temperature, but occurred sooner at the top than at 2-mm depth. Conversion at R _p ^max increased with temperature, allowing more of the reaction to occur prior to vitrification than at room temperature.