The changes in the property of general medical waste at different hydrothermal treatment temperatures and their potential application as fuel were examined to determine the utilization potential in the conventional incineration method via hydrothermal treatment. Among the different medical wastes studied, the fuel properties (e.g., calorific value) of cotton and gauze improved, while those of syringes and masks decreased, with increasing hydrothermal treatment temperature. For the hydrothermal treatment of medical waste, a temperature of approximately 230 °C was considered appropriate for fuel efficiency, while complying with legal standards. However, severe corrosion was observed in the hydrothermal treatment reactor for medical waste. The PVC found in medical waste was transformed to HCl during thermal decomposition; this HCl dissolved in water to lower the pH and cause strong corrosion inside the reactor. The results of the combustion test for medical waste performed with and without hydrothermal treatments showed that large volumes of the air pollutant CO were generated during ignition, which reduced as the combustion stabilized. For medical waste with hydrothermal treatment, the combustion time was extended owing to increased amount of fixed carbon and the decrease, and the CO concentration dropped to 60 ppm. No significant change was detected in NOx concentrations after the hydrothermal treatment.