Background and Aim: Diode laser is a great choice for soft tissue surgery. The diode laser is partially absorbed by hard dental tissues, making it safe for soft tissue surgery. This study aimed to compare the tissue thermal changes induced by three types of diode lasers at 810, 940, and 980nm wavelengths. Materials and Methods: In this in-vitro experimental study, using a diode laser device (continuous mode with a 400μm fiber tip) at each of the 810, 940, and 980nm wavelengths and powers of 1, 2, and 3W in contact mode, incisions with the length of 2cm were made on pieces of meat over a period of 10 seconds. The primary and secondary temperatures were measured using a thermocouple. Data were analyzed using two-way analysis of variance (ANOVA). Result: Tissue temperature changes induced by diode laser at 810nm/3W were significantly greater than that of 2W power. These changes were higher with 2W of power compared to 1W (P<0.05). Temperature changes induced by diode laser at 940nm/2 and 3W were significantly greater than that of 1W power (P<0.05). Temperature changes induced by diode laser at 980nm/3W were significantly greater than that of 2W power. Tissue temperature changes were higher with 2W of power compared to 1W (P<0.05). Conclusion: Diode laser (continuous mode with a 400µm fiber tip) at 3W of power and 980nm wavelength caused the highest rate of thermal changes. The 810nm diode laser with the power of 1W caused the slightest heat changes in the soft tissue.