Vibrio sp. strain JT0107 is one of the marine bacteria that secrete beta-agarases which catalyze the hydrolysis of agarose. The optimum culture conditions for the production of some beta-agarases have been determined. To increase agarase activity, aeration and a sufficient concentration of agarose are needed. One of the enzymes that the bacteria secreted into the culture medium was isolated and purified 39-fold using a combination of ultrafiltration and subsequent anion exchange column chromatography. The purified protein migrated as a single band (72 kDa) on sodium dodecyl sulfate polyacrylamide gel electrophoresis and its isoelectric point was 4.7. Amino acid sequence analysis revealed a single N-terminal sequence that had no sequence identity to other marine bacterial agarases. This novel enzyme was found to be an endo-type beta-agarase (EC 3.2.1.81) that catalyzes the hydrolysis of the beta-1,4 linkage of agarose to yield neoagarotetraose [O-3,6-anhydro-alpha-L-galactopyranosyl(1-->3)-O-beta-D-galactopyranosyl(1-->3)-D-galactose] and neoagarobiose [O-3,6-anhydro-alpha-L-galactopyranosyl(1-->3)-D-galactose]. The optimum pH and temperature for obtaining high activity of the enzyme were at around 8 and 30 degrees C, respectively. The enzyme did not degrade sodium alginate, lambda-carrageenan, t-carrageenan or kappa-carrageenan.