The present invention provides a hair treatment composition comprising a multi-arm polyethylene glycol derivative (A) that contains two or more functional groups that may be covalently bound to amines, a hair treatment agent comprising the composition, and a method for using the same. Optionally, the composition may further comprise a polyethylene glycol derivative (B), a biocompatible polymer (C), or both, wherein the derivative (B) and polymer (C) each contains one or more functional groups that may react with the functional groups of the derivative (A).