To investigate the origin of the Tsushima Warm Current Water, comparison of water property in the Korean Straits with the Taiwan Straits was done by using WOD05 data. In winter, temperature in the Korea Straits is colder than that in the Taiwan Straits. However, salinity is saltier in the Korea Straits. In summer, vertical variations of temperature and salinity in the Korea Straits are larger than those in the Taiwan Strait. High salinity water in the lower layer in the Korea Straits is always not found in the Taiwan Straits. This means that the origin of the high salinity water in the Tsushima Warm Current is not from the Taiwan Warm Current. Low salinity water in the upper layer in the Korea Straits is affected by Changjiang diluted water in the East China Sea.