Thelidium minimum (Massal. ex Nyl.) Arn. has been reported only once from Japan (Nylander 1890), originally as Verrucaria minima Massal. The original specimen studied by Nylander has been examined. Although it is very fragmentary material, the lichen can be easily distinguished from Thelidium minimum (Massal. ex Nyl.) Arn. in the morphology of the thallus and perithecia, and also the habitat. It is doubted whether the Japanese material belongs to the genus Thelidium. Thelidium minimum (Massal. ex Nyl.) Arn. is excluded from the lichen flora of Japan.