Hot-worked die steel is usually used under conditions requiring repeated heating and cooling. The repeated transformation of austenite to martensite or vice versa may occur on the surface of the hot-worked die. The characteristics of repeated martensitic transformation and the effects of preheating treatments have been investigated using a Formaster-F fully automatic transformation dilatometer. The results show that the volume fraction of martensite, f(m), formed in 750-degrees-C --> 20-degrees-C repeated cycling is changed with the cycling number, (N), and the preheating treatment has an important influence on the kinetics of martensitic transformation.