To obtain a hydrophilicity-imparting treating agent for polyester-based synthetic fiber products, which can give the treated polyester-based synthetic fiber products having good hydrophilicity and can further give dyed products having good color fastness to rubbing.

This hydrophilicity-imparting treating agent for the polyester- based synthetic fiber products comprises (A) a water-soluble polymer comprising starch and/or cellulose and a water-soluble ethylenic unsaturated monomer and (B) a polyoxyethylene-containing compound which has a number-average mol.wt. of 400 to 1,500 and comprises. (B1) a polyoxyethylene mono or di(8 to 22C) fatty acid ester having an HLB of 7 to 19 and/or (B2) a polyoxyethylenemono(8 to 20C)alkyl ether having an HLB of 11 to 18.