An earthworm protease, Lumbricus rubellus, was used to improve the dyeing properties of protein fibers such as wool and silk. The optimal condition for the activity of the earthworm pretense was about $40^{circ}C$ at pH 7. The wool and silk were treated with the protease extracted from an earthworm and the K/S values of the dyed wool and silk were measured using a spectrophotometer in order to compare the dye uptake. The pretense treatment enhanced the dyeing properties of protein fibers without severe changes in mechanical properties. The surface appearances of pretense-treated fibers were observed by microscopy analysis.