Detergents containing proteinase developed in Europe and U. S. A. are produced and used in Japan, but the advantage of such an agent seems to be questionable or negative in this country. Therefore, effectiveness of the agent and stability of the enzyme in the detergent solution were examined. Alkaline proteinase from Bacillus subtilis used in the detergent was more stable than other proteinases such as Molsin, Semialkaline proteinase, Trypsin, or Bromelain towards detergents, tripolyphosphate, and heat (40-50°). Activity of this alkaline proteinase was enhanced with 0.05-0.1% sodium salt of higher alkyl sulfate and 0.15-0.3% anionic detergents solution. Washing effect of detergents containing proteinase towards protein-soiled cloth was markedly accelerated by the combination of anionic or nonionic surfactant and proteinase. This combination had better effect than either the enzyme or the detergent alone. The cleansing action of proteolytic detergents at a low temperature (18°) decreased to one-half of that at 37°. Detergents containing proteinase had poor action on protein-soiled cloths added with rape-seed oil and starch.