A new kind of rare earth (RE) complex Tb(o-MBA)3phen was synthesized and used as an emitting material in electroluminescence. The material was doped into poly(N-vinylcarbazole) (PVK) as the emitting layer, which was made by spin coating. Three kinds of devices were fabricated with the structures: (A) ITO/PVK:Tb(o-MBA)3phen/LiF/Al; (B) ITO/PVK:Tb(o-MBA)3phen/BCP/AlQ3/LiF/Al ; (C) ITO/BCP/PVK:Tb(o-MBA)3phen/AlQ3/LiF/Al. Bright green emission could be obtained from device (A) and (C). The photoluminescence (PL) and electroluminescence (EL) mechanisms of this material had been investigated. Since there was an overlap between the PL spectrum of PVK and the excitation spectrum of the terbium complex, there should be a Fo rster energy transfer process between them. The excitation spectrum of PVK doped Tb(o-MBA)3phen system is similar with the excitation spectrum of PVK, yet it is different from that of Tb(o-MBA)3phen. So, the emission of Tb(o-MBA)3phen should partly come from the excitation of PVK while in the organic light-emitting diode (OLED), based on Tb(o-MBA)3phen, the emission mainly comes from the direct recombination of electron and hole. Bright green emission can be obtained from the optimized multi-layer device (C) and the highest EL brightness reached 180 cd/m2 at the voltage of 17 V.