The present invention provides a fiber-treating process wherein fiber is treated, in the presence of a polymerization initiator, with a fiber-treating composition containing (A) reactive protein synthesized by chemically bonding protein with a compound having polymerizable unsaturated group(s) or (A) grafted protein which has been produced by graft-copolymerizing (C) hydrophilic monomer having vinyl group(s) onto (A) reactive protein synthesized by chemically bonding protein with a compound having polymerizable unsaturated group(s), and (B) hydrophilic monomer having vinyl group(s). The process provides fiber imparted with moisture absorbability and releasability durable against washing, antistaticity, water absorbability, and dry hand.