A filmy fern specimen collected in Ishigaki-jima Island of the Ryukyu Islands located in southwestern Japan was identified as Hymenophyllum digitatum (Sw.) Fosberg (Hymenophyllaceae). It is a new record of the species for the flora of Japan as its northernmost distribution record in the world, and is also a new record in Japan for Hymenophyllum subgen. Sphaerocionium to which H. digitatum belongs. The nature of hairs observed in the present specimen matches that of H. digitatum, widely distributed in the Old World tropics, and the plastid rbcL sequences supported its inclusion in the presently circumscribed H. digitatum.