A polymeric fluorescent substance exhibiting fluorescence in the solid state, having a polystyrene reduced number-average molecular weight of 1.times.10.sup.3 to 1.times.10.sup.8, and comprising one or more repeating units of formula (1) and one or more repeating units of formula (8), --Ar.sub.1--(CR.sub.1.dbd.CR.sub.2).sub.n-- (1) --Ar.sub.2--(CR.sub.36.dbd.CR.sub.37).sub.n-- (8) wherein Ar.sub.1 represents a specific arylene or a divalent heterocyclic compound group, and Ar.sub.2 represent an arylene or a divalent heterocyclic compound group other than Ar.sub.1. By using the polymeric fluorescent substance, a high performance polymer LED can easily be obtained.