Degumming of waste silk with bacterium "SY-7" identified as Bacillus Megatarium was carried out in order to find out a efficient degumming of waste silk used in spinning. The results are as follows; 1. In fermenting on waste silk fiber, the optimum temperature of the strain selected was 31~36$^{circ}C$ and the optimum pH was 6.8~7.7. 2. In application of the selected bacterium "SY-7" for degumming, the strain has not only high capability for sericin decomposition but also shortens treating time by over 35 hours than that was carried out under natural degumming and baves are easily separated from cocoon layers or kibiso of waste silk. 3. In evaluation of purified silk fiber by the "SY-7", whiteness, lustre, handle of fibroin and separation of bave together on cocoon or kibiso are superior to goods fermented under natural condition. And the residual fats and fatty oils are also less than those of natural one. In tensile strength and elongation, however, there were no remarkble differences between two.rkble differences between two.