A method for producing a polymeric fluorescent substance characterized by comprising the step of contacting with an alkali a crude polymeric fluorescent substance that is fluorescent in a solid state and has a polystyrene equivalent number average molecular weight of 10.sup.4 to 10.sup.8 and one or more repeating units represented by the following formula (1): --Ar.sub.1--(CR.sub.1.dbd.CR.sub.2).sub.n-- (1) wherein Ar.sub.1 is an arylene group or heterocyclic compound group that is unsubstituted or substituted by one or more substituents; R.sub.1 and R.sub.2 each independently represent a group selected from the group consisting of a hydrogen atom, an alkyl group, an aryl group, a heterocyclic compound group and a cyano group, in which the aryl group and the heterocyclic compound group is optionally substituted by another substituent; and n is 0 or 1.