A novel aerobic bacterial strain, designated MK012T, was isolated from the phycosphere of Microcystis aeruginosa . MK012T appears to be Gram-stain-negative, non-motile and rod-shaped and has yellow pigments. Phylogenetic analysis using 16S rRNA revealed that this bacterium was most closely related to Flavobacterium buctense T7T (=JCM 30750T; 97.5 %), Flavobacterium dankookense ARSA-19T (=KCTC 23179T; 97.5 %) and Flavobacterium macrobrachii an-8T (=DSM 22219T; 97.3 %). The genome size and genomic DNA G+C content of MK012T were estimated at 3.3 Mbp and 37.6 mol%, respectively. The average nucleotide identity (ANI), average amino acid identity (AAI) and in silico DNA–DNA hybridization (dDDH) values of MK012T and the members of the genus Flavobacterium were found to be 71.8–78.3 %, 65.1–79.6% and 19.1–21.5 %, respectively. MK012T exhibited oxidase but no catalase activity. The cells grew at 14–36 °C (optimum, 25 °C), pH 5–10 (optimum, pH 7) and 0–0.4 % (w/v) NaCl (optimum, 0 % NaCl) in R2A medium. MK012T did not produce flexirubin-type pigments. The predominant cellular fatty acids of MK012T were determined to be iso-C15 : 0, iso-C15 : 0 3-OH, iso-C17 : 0 3-OH, and summed feature 9 (10-methyl C16 : 0 and/or iso-C17 : 1ω9c); MK-6 was identified as its only respiratory quinone. Its major polar lipids were determined to be phosphatidylethanolamine, two unidentified aminolipids, and two unidentified polar lipids. The genotypic and phenotypic characteristics indicate that MK012T (=KACC 21509T=JCM 33879T) represents a novel species of the genus Flavobacterium ; therefore, the name Flavobacterium phycosphaerae sp. nov. is proposed.