Two new species of the crab genus Actumnus Dana, 1851 (family Pilumnidae) are reported from the Ryukyu Islands, southwest Japan. Actumnus tsurukaii sp. nov. is similar to A. squamosus (De Haan, 1835), A. setifer (De Haan, 1835) and A. forficigerus (Stimpson, 1858) in possessing a poorly defined dorsal surface of the carapace with a coat of short setae, but differs in having relatively larger, fewer and more widely spaced conical granules or tubercles on the outer surfaces of the palms of both chelipeds. Actumnus uformis sp. nov. is similar to A. dorsipes Stimpson, 1858 and A. granotuberosus Garth & Kim, 1983 in having a prominently areolated dorsal surface of the carapace with a soft thick tomentum, but can be distinguished by the stronger areolation and the distinctly U-shaped protogastric region.