Numerous novel ingredients have been introduced for the hight functionality of whitening cosmetics. Tough the preliminary research, we have found water extracts Bombyx mori have high whitening efficacy. The results of the research for the whitening effect of Bombyx Mori L. are as follow 1. Bombyx Mori L. inhibited concentration dependently the generation of melanin increased by the stimulation of $alpha$-MSH and protoporphyrin IX, and $IC_{50}$ value was 8.3, 9.2 ${mu}M$ respectively. 2. Melanin increased by the stimulation of $alpha$-MSH and protoporphyrin IX was five to seven times superior in the inhibiting effect, compared with kojic acid used as positive control group. 3. Bombyx Mori L. did not have a decolorizing effect on melanin already generated. 3. Bombyx Mori L. was observed to have toxicity of over 100 ${mu}M$ for the mouse melanoma B16 cells. Therefore, These results suggest that water extracts of Bombyx mori have inhibitory activity against mushroom tyrosinase and inhibitory activity of melanin synthesis in B16 melanoma cells in vitro.