Recent progress of organic photochromic compounds for optical data storage media is described. Indispensable characteristics required for the compounds are the thermal stability of two chemical isomers, which are formed reversibly by photoirradiation, and fatigue resistant property. The requirements were achieved by the synthesis of a new type of photochromic compounds, diarylethenes with heterocyclic rings, which were designed according to the guiding principle based on the molecular orbital calculation of state correlation diagrams. The compounds were found to keep on storing the optical memory for more than 3 months at 80°C, and write/erase cycles of the compounds can be repeated more than 104.