A variety of novel light-emitting copolymers derived from 9,9-dioctylfluorene (DOF) and 2,1,3-naphthozoselenadiazole (NSeD) were prepared by the palladium-catalyzed Suzuki coupling reaction. The feed ratios of DOF to NSeD were 99.9:0.1, 99.5:0.5, 99:1, 98:2, 95:5, and 85:15. All of the polymers are soluble in common organic solvents and highly fluorescent in solid state. Devices based on the copolymers emit saturated red light, and the emission slightly red-shifted gradually with increasing NSeD's contents. The maximal external quantum efficiency of the polymer light-emitting devices (PLED) reaches 3.1%, and luminous efficiency is greater than 1.0 cd/A with emission maximum at 657 nm and Commission Internationale de L'Eclairage (CIE) coordinates of (0.64, 0.33). This is the highest efficiency with saturated red emission for a single-layer device with nonblend type emitter reported so far in the scientific literature. This indicates that the new EL polymers based on fluorene and naphthoselenadiazole are promising as a red emitter in polymer light-emitting displays.