Light emitting properties of several polyfluorene (PF) copolymers (P1–P4) and their blends have been investigated. Light emitting diodes were fabricated with the configuration of ITO/PEDOT:PSS/polymer/Ca/Al. The EL peak wavelengths were 421nm (violet), 505, 513nm (green) and 570nm (yellow) for PF copolymers and 510, 535nm (green) for P1/P2 and P1/P3 blends, respectively. Förster energy transfer in the photoluminescence and electroluminescence of the polymer blends P1/P2 and P1/P3 was studied. The LED using the polymer blend P1/P2 showed a turn-on voltage of 2.5V and a brightness of 5×10 4 cd/m 2 at 7V. The highest external quantum efficiency was observed to be 3.71% at 5V. Upon addition of 20wt% of the green emitter P2 to the violet emitter P1, the device efficiency increased from 1.18 to 3.71%.