A mixture of extracellular carrageenases was isolated from the cell-free medium of a culture of marine Cytophaga sp. 1k-C783 grown on ZoBell 2216 E broth with 0.1% commercial carrageenan. A single active peak of κ-carrageenase was separated and purified from the mixture by ammonium sulfate precipitation, ion-exchange chromatography, and Sephadex G-200 gel filtration chromatography. Molecular weight of the purified κ-carrageenase was estimated as 100, 000 by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). The purified κ-carrageenase had pH optimum 7.6 and temperature optimum 25C.