Although CO 2 laser irradiation can decrease enamel demineralization, thermal damage to the surface is a common side effect. The occurrence of fissures and cracks may compromise in vivo application. Therefore, the aim of the present study was to find CO 2 laser (10.6 ??m) parameters resulting in maximum caries- preventive effect with the lowest thermal damage. Five low fluences of 0.12, 0.29, 0.39, 0.50 and 0.60 J/cm 2 combined with high repetition rates of 500, 154, 167, 182, 187 Hz, respectively and 10 ??s pulse duration were chosen for the experiments. 78 bovine enamel cubes were divided into 5 laser groups and one control. After treatment the samples were submitted to an 8-day pH-cycling regime. Demineralization was assessed by lesion depth measurements with a polarized-light microscope. The temperature rise at the enamel surface and the propagation into deeper layers were calculated using a finite element model. Surface morphology was evaluated by SEM. All laser groups resulted in statistically significant lower lesion depths than the control group (ANOVA; p < 0.05). Morphologically, the two lowest fluences resulted in no surface changes. The calculated temperature rise at 1.5 mm depth was less than 5 ?? C in all groups. In the present in vitro study irradiation with 0.12 J/cm 2 , 500 Hz and 2500 pulses of CO 2 laser increased enamel caries resistance without causing undesirable surface damage or excessive temperature rise.