High temperature properties such as hot hardness and thermal fatigue resistance of high speed steel roll of hot finishing mill have been investigated. Two kinds of roll having compositions, Fe-1.75%C-5.9%Cr-1.74%Mo-4.94%V-2.03%W(A specimen) and Fe-2.27%C-8.86%Cr-2.91%Mo-3.92%V-1.86%W(B specimen)were prepared for investigating the microstructure and crack propagation mode. A specimen has greater amounts of M_7C₃type carbides and less amounts of MC type carbides in comparison with B specimen. Hot hardness showed sudden decrease over 400℃, resulting in the hardness decrease of 50% at the temperature of 600℃, and showed little variation with time at 500℃ and 800℃. Thermal crack was developed at 550℃ in A specimen and 600℃ in B specimen.