Clathrate hydrates formed with nonflammable gases may be suitable for use as fire extinguishing agents because the dissociation of the hydrates decreases the temperature in the flame base and the nonflammable gases released from the dissociated hydrates prevent the supply of oxygen to the flame base. In the present study, we performed experiments to extinguish pool flames using the hydrate crystals formed with carbon dioxide. From the experimental result, the critical mass of CO2 hydrate to extinguish the flame was found to increase when the size of the pool flame is increased. The critical mass to extinguish the same size flame of ordinary ice and dry ice was also measured. These results showed that the CO2 hydrate can extinguish the pool flame with less water as compared to ordinary ice and less releasing of the CO2 as compared to the dry ice.