The aim of this study is to evaluate increases in temperature on the external root surface during endodontic treatment with three different rotary file systems. Fifty human mandibular first premolars with single root canal were selected. All root canals were instrumented using a size 20 H file, and the canals were irrigated with 5% sodium hypochlorite solution. The samples were randomly divided into the following three groups of 15 teeth: Group 1: The Protaper Next Rotary Files X1 and X2; Group 2: The Mtwo rotary File 20/06 and 25/06 Group 3: The Hyflex rotary File 20/06 and 25/06. During the preparation, the temperature changes were measured in the middle third of the roots using a noncontact infrared thermometer. The temperature data were transferred from the thermometer to the computer and were observed graphically. Statistical analysis was performed using the oneway ANOVA analysis of variance at a significance level of 0.05. The increases in temperature caused by the Hyflex rotary file system were lower than those of the other files. The Mtwo rotary file showed the highest temperature increases. However, there were no significant differences were noticed between the Protaper Next and Hyflex rotary files in terms of temperature increase during root canal preparation. Mean temperature increases no higher than 3.4ºC were recorded for any of the system examined, which indicates that these instruments are safe for the surrounding periodontal tissues.