The pure BiFeO3 (BFO) and (Er, Mn) co-doped Bi1−xErxFe0.95Mn0.05O3 (x = 0, 0.05, and 0.10) nanoparticles were synthesized by a sol–gel method. The effect of (Er, Mn) co-doping on the structural and multiferroic properties of BFO nanoparticles were systematically investigated. The results showed that the value of x had a significant influence on the multiferroic properties of the synthesized nanoparticles. Compared with pure BFO sample, the leakage current density of all the (Er, Mn) co-doped samples is much smaller than that of pure BFO. The best magnetic properties are obtained in the x = 0.10 sample, where the remanent magnetization (Mr) is as high as 0.426 emu/g, and the coercive field (Hc) is up to 5.91 kOe. The present work provides an effective method to enhance the multiferroic properties of BFO.