In an effort to isolate a bacterium producing chondroitin sulfate (CS), a marine bacterium, KS-1, which produces mucopolysaccharides, was isolated from seawater and identified as Marinobacter sp. based on analyses of its morphological and biochemical traits and 16S rDNA sequence. Agarose-gel electrophoresis showed that the KS-1 strain produces a CS-like mucopolysaccharide. Structural analysis using Fourier transform infrared spectroscopy revealed that the structure of the CS-like mucopolysaccharide produced by Marinobacter sp. KS-1 is similar to that of dermatan sulfate (CS B). However, the molecular mass of the CS-like mucopolysaccharide is higher than that of standard chondroitin sulfates. Considering the above results, we conclude that the Marinobacter sp. KS-1 produces a CS-like mucopolysaccharide that differs somewhat from CS B in molecular mass.