A polymeric fluorescent substance showing fluorescence in the solid state, having a polystyrene reduced number-average molecular weight of 10.sup.3 to 10.sup.8, and comprising one or more repeating units of formula (1) and one or more repeating units of formula (2) which is different from formula (1), ##STR00001## exhibits strong fluorescence and/or excellent charge transporting property, and a high performance polymer LED which can be driven at low voltage and high efficiency is obtained.