A heat-resistant ferritic cast steel having excellent thermal fatigue resistance, consisting, by weight, of 0.25 to 0.45% C, 0.3 to 2.0% Si, not more than 1.0% Mn, 17 to 22% Cr, at least one kind selected from the group consisting of not more than 6% Co and not more than 1.5% Ni, the amount of % Co+3 % Ni being in the range of 1 to 6%, 0.006 to 0.1% of at least one kind selected from the group consisting of Y and rare earth elements, and the balance Fe and incidental impurities, the ferritic cast steel being composed of a structure in which .alpha. ferrite and M.sub.23 C.sub.6 carbide are dispersed in .delta. ferrite. With this specific composition, even at high temperatures, there can be maintained the structure which has the .alpha. ferrite and the M.sub.23 C.sub.6 dispersed in the .delta. ferrite, with the result that there is obtained an excellent thermal fatigue resistance, and in this structure, the transformation under heating will not occur even at a temperature of about 1,000.degree. C. The steel of the present invention is particularly suited for a turbo rotor casing, an exhaust manifold, etc., of an automobile.