The photochromism of three diarylethene derivatives was examined on porous aluminum oxide. Upon alternate irradiation with UV and visible light, the diarylethenes having thiophene rings decomposed easily, while a derivative having benzothiophene rings underwent a reversible photochromic reaction. The decomposition started from the closed-ring isomers of the dithienylethenes. The decomposition mechanism was discussed based on the oxidation potentials of the compounds.