To provide a durable antistatic agent for synthetic fibers, which is easily processed with a generic processing machine, exhibits a little hand hardening due to a treatment, and is excellent in durability and antistatic property.

The durable antistatic agent for synthetic fibers is obtained by polymerizing a monomer mixture consisting of (a) (meth)acrylic acid polyethylene glycol monomer or a (meth)acrylic acid alkoxy polyethylene glycol monomer in an amount of 25-100 wt.% and (b) another copolymerizable ethylenically unsaturated monomer in an amount of 0-75 wt.% (provided that (a)+(b)=100 wt.%) in the presence of a block-type urethane prepolymer including ethylene oxide chains.