To develop cast-iron brake disks with high heat resistance to thermal shock loading, three candidate materials were developed. The main components were Fe, C, Si, Mn, Ni, Cr, Mo, Cu and Al. The mechanical and thermal properties of the candidates were measured. Thermal fatigue tests were then carried out using equipment developed by the authors. The possible temperature range of the testing equipment was $20^{circ}C{sim}1500^{circ}C$. Cylindrical solid specimens ${phi}20{ imes}80mm$ were heated by an induction coil and cooled in water. At an interval of 20~30 thermal cycles, the surfaces of the specimens were examined with a digital microscope to check for thermal cracks. To quantify the total length of the cracks, an image analyzing program capable of measuring the length of cracks on micrographs was developed. It was found the fatigue lifetime of cast iron could be increased by regulating its composition and metallurgical structures.