A waterproof thermometer for monitoring a food temperature during a cooking process includes a rechargeable battery for supplying power, a thermal sensor for measuring the food temperatures, and a processing unit for wirelessly transmitting data via an antenna. The waterproof thermometer further includes a first conductive part for containing the thermal sensor, the processing unit, and the rechargeable battery, a first insulating part for containing the antenna, a second insulating part, and a second conductive part. The first insulating part is surrounded by the second insulating part, and separated from the second insulating part by an air filled gap. The first conductive part, the first insulating part and the second conductive part form a first hermetic shell for providing waterproof function. The first conductive part, the second insulating part, and the second conductive part form a second hermetic shell for providing protection to the first insulating part from being damaged.