A pineapple protease, bromelain, was used to improve the dyeing properties of protein fibers such as wool and silk. The optimal condition for the activity of the pineapple protease was about $60^{circ}C$ at pH 7. The wool and silk were treated with the protease extracted from a pineapple and the K/S values of the dyed wool and silk were measured using a spectrophotometer in order to compare the dye uptake. The protease treatment enhanced the dyeing properties of protein fibers without severe changes in mechanical properties. The surface appearances of protease-treated fibers were observed by microscopy.