Abstract: In order to provide strains which have a high enzyme yield, the original strain Bacillus licheniformis HDYM- 04 was isolated naturally and then treated with ultraviolet ray. The best mutation condition was determined to expose the strain to the ultraviolet source at 50 cm for 10 s based on the fatality rate. The total strain mutation rate was 76.11%, the positive mutation rate was 54.60%, and the negative mutation rate was 20.92%. A stable β-mannanase producing strain Bacillus licheniformis U2-12 was obtained with the enzyme activity being 242.19% of the original strain. The results can provide superior enzyme production strains for the following test and production practice, and references for studying the effect of ultraviolet ray on β-mannanase gene.