The first step in the hydrolysis of cuprammonium rayon with endocellulases was examined and the results were compared with those of hydrolysis with a cellulase complex. Mechanical agitation during endocellulase treatment was effective for the separation of the oligomers from the substrate. The endocellulases removed the intermediately ordered regions in the disordered matrix, The crystalline regions were negligibly affected by the endocellulases, while the cellulase complex considerably deaggregated the surface of the crystallite. Toe endocellulases enhanced the brittleness of the fabric more than did the cellulase complex, It was assumed that the hydrolysis with the endocellulases proceeded without molecular deaggregation of the fiber,