Polyhedral oligomeric silsesquioxanes (POSS) anchored to poly(2-methoxy-5-(2-ethylhexyloxy)-1.4-phenylenevinylene) (MEH-PPV) (MEH-PPV–POSS), and to poly(9,9-dihexylfluorenyl-2,7-diyl) (PFO) (PFO–POSS) were synthesized. Compared with the corresponding parent polymers, MEH-PPV and PFO, MEH-PPV–POSS and PFO–POSS have better thermal stability. MEH-PPV–POSS and MEH-PPV have identical absorption and photoluminescent (PL) spectra, both in solution and as thin films. They also have identical electroluminescent (EL) spectra. Devices made from MEH-PPV–POSS exhibit higher brightness (1320 cd m–2 at 3.5 V) and higher external quantum efficiency (ηext = 2.2 % photons per electron) compared to MEH-PPV (230 cd m–2 at 3.5 V and ηext = 1.5 % ph el–1). Compared with PFO in the same device configuration, PFO–POSS has improved blue EL emission and higher ηext.