Forefoot characteristics of the Ryukyu long-furred rat, Diplothrix legata, in the Amami-oshima, Tokunoshima, and Okinawajima Islands of the southern part of Japan (the Nansei Archipelago), were analyzed morphologically considering its arboreal lifestyle. The presence of a nail on the pollex was confirmed and seemed to be regarded as an arboreal feature, based on the presence of nails in other arboreal murids reported in previous studies. In addition, a linear palmar groove was confirmed between the interdigital pads and the thenar-hypothenar pads. We tried to allow the forefoot to take hold of a thin stick at this groove; the stick fit well in the groove, and it seemed to be possible to grip by the fingers except for pollex. Thus, the sizes and positions of palmar swollen pads forming the linear groove were considered to be useful for gripping a thin twig in an arboreal lifestyle. In addition, the entire unguis size tended to be larger in Okinawajima Island than in Amami-oshima Island as a geographical variation.