This study characterizes three Anabaena strains and 5 Trichormus strains isolated from Korean waters and 3 Anabaena flos-aquae strains procured from the UTEX based on morphological features and molecular analyses. The Anabaena and Trichormus isolates were morphologically assigned to A. variabilis Kützing and T. variabilis (Kützing ex Bornet et Flahault) Komárek et Anagnostidis, respectively. The Anabaena and Trichormus strains differed significantly in the mean length of their vegetative cells. The 16S rRNA genes from the Anabaena strains showed a 100% identity to that from A. variabilis ATCC 29413, while the 16S rRNA genes from the Trichormus strains showed a 99.9% identity to that from T. variabilis GREIFSWALD. The overall topology was in agreement for the 16S rRNA gene and cpcBA-IGS trees in the both tree-constructing methods. In a neighbor-joining tree based on the 16S rRNA gene, the 3 Anabaena strains were asso-ciated with A. variabilis, the 5 Trichormus strains with T. variabilis, and the 3 Anabaena (UTEX) strains were with Nostoc. To date, this is the first report on A. variabilis and T. variabilis strains originating from Korea.