This research shows the slagging propensity of 5 coals used in power plant in Korea. We evaluated the slagging propensity by using a thermo-mechanical analyzer (TMA) and ash fusion temperature (AFT).The newly proposed slagging index(BHEL index) has been compared with the existing slagging indices for 5 coal ash samples. Consequently, It was shown that the BHEL indices of 4 coals excepting Moolarben is similar to the existing traditional indices of those coals.