Provided is a polymeric fluorescent substance comprising a copolymer which has a substituent containing a specific aromatic amine structure below in the side chain, ##STR00001## wherein X.sub.1 is a divalent hydrocarbon group; Ar.sub.2 is an arylene group or the like; Ar.sub.3 and Ar.sub.4 independently represent an aryl group or the like. The polymeric fluorescent substance is preferably used for a light emitting layer of a polymer LED having high luminance and high light emitting efficiency.