This study reports the isolation of a bacterium capable of degrading agar and the characterization of its agarase. An agar-degrading marine bacterium JS-1 was isolated using Marine agar 2216 media from seawater collected from the seashore of Angolpo, Changwon, Gyeongnam Province, Republic of Korea. An agar-degrading bacterium was named as Tenacibaculum sp. JS-1 by phylogenetic analysis based on 16S rRNA gene sequence. The extracellular crude agarase was prepared from the culture media of Tenacibaculum sp. JS-1 and used for characterization. Relative activities at 20, 30, 40, 50, and 60℃ were 39, 73, 100, 74, and 53%, respectively. Relative activities at pH 5, 6, 7, and 8 were 46%, 67%, 100%, and 49%, respectively. Its extracellular agarase showed maximum activity (164 U/l) at pH 7.0 and 40℃ in a 20 mM GTA buffer. The residual activities after heat treatment at 20, 30, and 50℃ for 30 min were 84, 73, and 26% or more, respectively. After 2 h heat treatment at 20, 30, 40, and 50℃, the residual activities were 80, 64, 52 and 21%, respectively. Thin layer chromatography analysis suggested that Tenacibaculum sp. JS-1 produces extracellular β-agarases that hydrolyze agarose to produce neoagarooligosaccharides, including neoagarohexaose (12.3%), neoagarotetraose (65.1%), and neoagarobiose (22.6%) at 6 h. Tenacibaculum sp. JS-1 and its β-agarase could be valuable for producing neoagarooligosaccharides with a variety of functional properties. These properties include inhibiting bacterial growth, slowing down starch degradation, and whitening, which are of interest for pharmaceuticals, food, cosmeceuticals, and nutraceuticals.