'Usul' is a traditional medicinal herb, which has anti-inflammatory activities is distributed in India, Nepal, China, Korea, Japan. Korea pharmacopeia listed 'Usul' as either a species of Achyranthes japonica (Miq.) Nakai or A. bidentata Blume. Recent taxonomic studies in China and Japan delimited these taxa as two varieties, A. bidentata Blume var. bidentata and var. japonica Miq. A multivariate morphometric study of Achyranthes bidentata complex was undertaken to assess the entities of taxa that usefully could be recognized. Five quantitative characters were reviewed and analyzed with 293 specimens from Korea. The univariate analysis of inflorescence length, interval between florets, angle between floret and floral axis indicated that ranges among all taxa were continuous. However, quantitative characters of membrane size and the number of hairs within 4 were useful to identify two varieties. In PCA, the first three principal components accounted for 89.4% of the total variance. PCA revealed that var. bidentata showed distinctions in morphological attributes from var. japonica entity. Therefore, continued recognition at the infraspecifc level for these taxa is supported.