Oak wilt disease caused by Raffaelea quercus-mongolicae is one of the serious diseases in Korea. Infected trees showed wilting and discolourations on the cambium when the bark of a tree is peeled, since it deters moisture migration. Raffaelea quercus-mongolicae is vectored by Platypus koryoensis. In this regard, it was assumed that there might be a positive correlation between the number of gallery generated by P. koryoensis and the level of damage on the infected tree by the oak wilt disease. In order to link the occurrence of dead oak trees with the number of galleries produced by P. koryoensis, five regions (Incheon, Anyang, Gwangmyeong, Icheon and Gimhae) were selected in Korea. The number of galleries on Mongolian oaks produced by attack of P. koryoensis was counted in four directions between 50cm and 100cm from the ground level. Furthermore, Vegetation was investigated from the area where the oak wilt disease occurred, and a data logger was set up to collect data including temperature and relative humidity in each region at the elevation between 100~200m. A significant difference was observed in the number of galleries made by the insect vector between dead trees and trees infected with oak wilt disease, while no difference was observed from the vegetation on the area investigated. We will further investigate as to whether climate factors might contribute to the density and the successful invasions of the insect vector to the oak trees.