Objective: The aim of this study was to assess the application of Er:YAG laser root canal preparation using two fiber tip systems. Background Data: Previous studies have not shown the thermal effect of Er:YAG laser using cone-shaped fiber tip. Materials and Methods: The ability of Er:YAG laser to enlarge root canals at a pulse energy set at 30 or 20 mJ and constant pulse rate of 10 pps (pulses per second) was tested. A cone-shaped (84 degrees top angle) or a flat fiber tip of Er:YAG laser was used for comparison. Four groups of 15 artificial root canals with fixed dimension were prepared from bovine teeth. Irradiation was accompanied by sterilized distilled water spray (2 mL/min). The temperature changes on the root surface were recorded with an infrared apparatus, and the thermal images were captured with a thermocamera. The morphological changes of irradiated root canals were examined by a scanning electron microscope (SEM). Results: The mean temperature rises were 9.4degreesC and 7.1degreesC with the cone-shaped fiber tip at a pulse energy of 30 and 20 mJ, respectively, and were 11.0degreesC and 6.5degreesC with flat fiber tip at a pulse energy of 30 and 20 mJ, respectively. Marked difference in temperature change between the cone-shaped and flat fiber tips was noted at pulse energy of 30 mJ, but not at 20 mJ. The thermal distribution using the cone-shaped fiber tip (in contrast to the flat tip) had an elliptical shape around the fiber tip and was limited to the apical end of the root canals. SEM observation found that irradiation with cone-shaped fiber tip (in comparison to the flat tip) produced a cleaner surface. Conclusion: Our results suggest that the cone-shaped fiber tip of Er:YAG laser produced fewer thermal effects and morphological changes as compared to the other type of fiber tip.