A marine bacterium SD8 producing thermostable alkaline serine nonmetal protease was isolated from sea muds in Geziwo Qinhuangdao sea area, China. The crude extracellular protease produced by the isolate had optimal activity at about 60℃. The enzyme was stable at 20-50℃ and retained 58 and 43% of its initial activity after heating for 1 h at 60 and 70℃, respectively. The protease was highly active from pH 7.0-11.5 and stable from pH 7.0-11.0, with an optimum at pH 10.0. The activity was totally lost in the presence of PMSF(phenylmethylsulfonyl fluoride) and slightly increased in the presence of EDTA, suggesting that the preparation contains serine-protease(s) and nonmetal protease(s). Moreover, the crude protease was activated by the presence of 5mM Ca2+, Mn2+, Zn2+ and Cu2+. Furthermore, the enzyme showed excellent stability towards anionic surfactant SDS(5mM). In addition, the enzyme was also stable towards oxidizing agents, retaining 89% of its initial activity after 20 min incubation in the presence of 1% H2O2. The crude protease was found to be stable in the presence of several organic solvents too. The marine bacterium strain SD8 selected is thus promising thermostable alkaline protease producers for industrial use.