We used Brevibacterium sp. JCM 6894, which was isolated from seawater, to degrade the water-soluble fraction of jellyfish. After 27 h of incubation, the protein content in the supernatant was reduced from 1.97 to 1.31 mg/ml with an increase in cell yield of 0.40 mg cell protein/ml. The missing protein content in the fraction was 0.26 mg/ml. By the cell growth, the content of NH3 was increased from 0.38 to 4.57 μmol/ml. The value of chemical oxygen demand, which is a marker of remaining organic compounds in the fraction, was reduced from 890 to 431 mg O2/liter.