In this study, we report the first occurrence of the filamentous green macroalga Basicladia okamurae (Cladophorales, Chlorophyta) from Korea. This species was originally described as Chaetomorpha okamurae by Ueda in 1932 in Japan and was later transferred to the genus Basicladia. Basicladia okamurae (Ueda) Garbary 2010 has also been found in China and the Netherlands, supported by morphological and molecular evidence. We collected several filamentous green algal individuals from the freshwater stream Sanhocheon (Changwon-si, Republic of Korea) and identified the species as B. okamurae based on morphological characteristics and nuclear ribosomal large subunit (LSU) rDNA sequence analysis. The LSU rDNA sequences of the Korean B. okamurae exhibited 99.8-100% similarity with those of B. okamurae deposited in GenBank (NCBI) and could be distinguished from other species in the order Cladophorales, which showed less than 91.2% similarity. Based on this morphological and molecular evidence, we confirm the species identification as an unrecorded B. okamurae (Ueda) Garbary.