Xylanase is the enzyme complex that is responsible for the degradation of xylan; however, novel xylanase producers remain to be explored in marine environment. In this study, a Streptomyces strain M11 which exhibited xylanase activity was isolated from marine sediment. The 16S rDNA sequence of M11 showed the highest identity (99 %) to that of Streptomyces viridochromogenes. The xylanase produced from M11 exhibited optimum activity at pH 6.0, and the optimum temperature was 70 °C. M11 xylanase activity was stable in the pH range of 6.0-9.0 and at 60 °C for 60 min. Xylanase activity was observed to be stable in the presence of up to 5 M NaCl. Antibiotic-resistant mutants of M11 were isolated, and among the various antibiotics tested, streptomycin showed the best effect on obtaining xylanase overproducer. Mutant M11-1(10) isolated from 10 μg/ml streptomycin-containing plate showed 14 % higher xylanase activities than that of the wild-type strain. An analysis of gene rpsL (encoding ribosomal protein S12) showed that rpsL from M11-1(10) contains a K88R mutation. This is the first report to show that marine-derived S. viridochromogenes strain can be used as a xylanase producer, and utilization of ribosome engineering for the improvement of xylanase production in Streptomyces was also first successfully demonstrated.