A study was made of the effects of alloying elements on microstructural factors of nine high speed steel (HSS) rolls manufactured by centrifugal casting method. Particular emphasis was placed on the role of hard carbides located along solidification cell boundary and the type of the martensite matrix. Microstructural observation, X-ray diffraction analysis, and hardness measurement were conducted on the rolls to identify carbides. Various types of carbides mostly segregated in the intercellular regions were dependent upon alloying elements and their amount, and played an important role in overall roll hardness. The effects of alloying elements were analyzed on the basis of the liquidus surface diagram, suggesting that the proper contents of carbon, tungsten, molybdenum, chromium, and vanadium were 1.9-2.0%, 3-4%, 3-4%, 5-7%, and 5-6%, respectively.