The effects of the addition of Pr₆O₁₁ nanopowder on the critical current density (J_c), irreversibility field (H_irr) and upper critical field (H_c2) of the MgB₂ bulks prepared by a Mg-diffusion method were investigated. The experimental results showed that J_c, H_irr and H_c2 of the MgB₂ bulks have been enhanced systematically by Pr₆O₁₁ nanopowder doping, but the superconducting transition temperature (T_c) was little affected. At 20 K in a self-field, the J_c value for the 1 wt.% Pr₆O₁₁-doped MgB₂ sample was 3.61×10₅A/cm₂, which was nearly five times larger than the undoped sample. In addition, at 10 K, the H_c2 and H_irr of the bulk increased by 1.9 T and 2.6 T, respectively. The Pr₆O₁₁-dopingmechanism on superconductivity and flux pinning was also discussed.