Highly increased usage of high performance engines has created a tremendous demand for exhaust components which can resist severe heat enviroments to nearly 1273 K. Such cast irons as high Si and austenitic ductile cast irons are not able to meet those requirements. Then the authors investigated some alloy steels to be able to improve thermal deformation on the basis of ferritic heat-resistant 18 % chromium steel having excellent oxidation resistance. As a consequence of these effforts, we have developed a new heat-resistant cast steel composed of 0.2 % C-18 % Cr-Ni-W-Nb for exhaust components required especial resistance to thermal deformation.