It was found that globulin fractions had extracted muscle tissues of rabbit and of silkworm by neutral buffer had proteolytic activity ; there are optimum regions at pH 3.0 and 8.8 in the use of silkworm preparation and at pH 3.8 and 8.3 in the use of rabbit preparation. These optimum temperature are 35℃ in either preparation. It was concluded that silkworm preparation contained a protease with SH group from effects for cyanate and monoiodoacetate.