Abstract: To obtain amylase from marine source,we bred a strain Streptomyces roseofulvus A46 screened from intertidal zone of Zhoushan by ultraviolet and DES mutation.The enzyme activity reached 105.6 U/mL by flask culture,which was 213.3% higher than that of the parent strain,A46.Descent of only 3.6% in enzyme activity of the mutant was observed after ten times of subculture,and the obtained mutant is a relatively stable strain.The optimized fermentation conditions were formulated using Plackett-Burman design and response surface analysis(RSA):culture temperature was 33 ℃;inoculum size was 2.25%;salinity was 23.4;initial pH was 8.0;rotating speed was 200 r/min;medium volumes was 20%;starch content was 0.5%;incubation time was 72 h.Researches show that the enzyme activity was 125.8 U/mL under the optimum condition,which was 19.1% higher than that of non-optimized condition.