To produce the subject structure such as a woolen (blend spun) woven fabric, etc., rapidly undergoing the weight-reduction treatment at a high weight reduction ratio and having an extremely soft touch feeling by carrying out the weight-reduction treatment of a fiber structure containing animal hairy fibers with a weight-reduction treating agent containing a proteolytic enzyme and a reducing agent.

The weight-reduction treatment of a fiber structure containing animal hairy fibers such as wool is carried out with a weight-reduction treating agent containing (A) a proteolytic enzyme (papain, trypsin, a proteolytic enzyme derived from Bacillus subtilis, etc.) and (B) a reducing agent (sodium sulfite, sodium thiosulfate pentahydrate, etc.). Thereby, the hydrolytic rate of the proteolytic enzyme can remarkably be raised while minimizing the deterioration in strength of the animal hairy fibers.