Protease is mixtured in detergent to remove protein-soil easily. It must not act on the any fiber except protein-soil during laundry. So the purpose of this study is to investigate how protease is affect the fiber, particulary the protein-fiber. For this purpose, silk, wool and nylon are selected as samples, and the extent of the damage was estimated as tensile strength and surface condition (that is fibrillation). The results are as follows. The tensile strength of fiber treated with protease were lowered at enzyme concentration 0.1%, temperature 4$0^{circ}C$ , and, as washing time was longer, it was lowered more. And it was showed that the surface of fibers were fiblliated by protease during washing. From this results, it was found that protease damaged protein-fiber. The damage of silk was the largest of all, and wool was less damaged than silk, because it has the scale (cuticle) on the outside. Additionary, an influence of surfactant on damage of fiber was little about three fibers, but, the fibers were damaged more by the binary nonionic-surfactant and protease mixture than by protease only.