The mutagenesis effects on the yield of amylase have been investigated with ,Bacillus subtilis, irradiated by γ-rays and fast neutrons in once or twice irradiation at various dose rates and total irradiation doses. Several parameters such as flat transparent circle, colony diameter, transparent circle diameter and the ratio of flat transparent circle to colony diameter (HC) are used to estimate the radiation mutation of ,Bacillus subtilis,. A series of results has been obtained as (1) Irradiation both with neutrons and γ-rays could make ,Bacillus subtilis, mutationed to produce high-yield amylase effectively. (2) The average colony diameter of ,Bacillus subtilis, irradiated by γ-rays or fast neutrons is smaller than that of control group at various total doses and dose rates. And their colony diameter becomes smaller slightly with the increment of γ-rays irradiation dose. (3) After the second neutrons irradiation, the values of average colony diameter, the biggest colony diameter, average transparent circle diameter and the biggest transparent circle diameter of all mutationed ,Bacillus subtilis, exceed that of original strains greatly. (4) Three kinds of mutationed ,Bacillus subtilis, strains with high-yield amylase have been screened out, in which two strains can produce high-yield amylase steadily after 15 times breeding. Their biggest colony diameter, the biggest transparent circle diameter and the biggest HC value are up to 8.32 mm, 22.38 mm and 5.39 respectively.