The sea anemone Capnea japonica (Carlgren, 1940) was described based on two specimens collected in 1914 off the coast of Misaki, Sagami Bay, Japan. Besides the two syntypes, no further specimens are known to have been collected. The original description of C. japonica is brief, and, therefore it is difficult to identify the species based on the available information. In 2014, we collected a single specimen of Capnea Gosse, 1860 from around the type locality of C. japonica and examined its morphological characters, such as the external features, cnidome, and musculature, and then compared it with the syntypes of C. japonica. The characteristic form of tentacles, size and distribution of cnidae, and very strong sphincter muscle in our specimen were a good match to the original description and to the results of examining the syntypes. Based on the topotype and syntypes, we redescribe C. japonica and show its phylogenetic position with newly obtained DNA sequencing data.