The silkworm eggs and silkworm larvae were treated with X-Rays, and then the mutations were induced artificially. The results obtained are as follows: 1. The best range of time was from 1 to 1.5 seconds to induce the mutations. 2. The silkworm-eggs treated with X-rays were almost malformes, unmoulting or radiation sick. 3. Silkworm-eggs laid by the moth-fed on penicillin in 1963 were also treated with x-rays. Many useful ones were found from them. 4. There is the possibility of silkworm improvement by inducing mutations with x-rays. Further studies are therefore needed in this field.