Inadvertent thermal injury can occur in pediatric patients under general anesthesia during knee arthroscopic surgery. Here, we report the case of a 10-year-old boy who underwent knee arthroscopic surgery under general anesthesia. After the surgery, he complained of pain in the left lower part of his chin and was diagnosed as having a thermal burn. At three-month follow-up, he recovered without any abnormalities except mild hypertrophy of the wound area. Although rare, arthroscopic surgery has the potential to cause thermal injury from the light source. We recommend that the light source should be connected to the arthroscope before switching the power on and disconnected after a considerable time of switching the power off when not in use.