On the six hypereutectoid alloy steels, the effects of austenitizing temperature and holding time on the Ms point have been investigated by dilatometric method. In view of the fact that the lowering of the Ms point results from dissolution of the carbide in the austenite and when dissolution is finished the Ms point reaches the constant value, activation energy of carbide dissolution for the three Cr steels with different carbides was derived from the relation between the time required for the Ms point to reach the constant value at each austenitizing temperature and the austenitizing temperature. Their values were 74300 cal/mol (1.02%C and 1.99%Cr: θ carbide), 55600 cal/mol (0.96%C and 9.37%Cr: η carbide) and 50700 cal/mol (0.26%C and 12.97%Cr: ε carbide). From the results obtained, it has been considered that the process of carbide dissolution relates to the compositions of the carbide and the neighbouring austenitic matrix and to the quantity of the dissolved carbide and moreover the mechanism of carbide dissolution is not a simple diffusion process. In the case of addition of 3.82%W, 0.50%Ti and 1.40%V respectively to 1%C∼2%Cr steels, the Ms points became higher as a whole than in the case of no addition, especially remarkable in addition of vanadium. Their behaviors may have revealed the dependence of carbon content of the austenite on the solubility of the special carbide formed by each additional element and moreover the effect of each additional element dissolved in the austenite on the Ms point.