The influence of different boron precursor powders on the critical current density of MgB2 superconductor with added Ni–Co–B nanoparticles is investigated. Different types of boron have different morphologies, particle sizes and impurity content, all of which have a strong impact on the critical current density (Jc). The boron samples investigated in this study include three different boron powders: semicrystalline boron (denoted as SC), with nanosized particles and high purity (99%) supplied from Specialty Materials, Inc. (USA); amorphous boron (denoted as AB), with nanosized particles and high purity (99%) supplied from Russia; and finally pure crystalline boron (denoted as CB), with micron-sized particles and 96% purity supplied from Tangshan WeiHao (China). The MgB2 samples made from AB showed the best improvement of critical current with 2.5 wt.% Ni–Co–B doping; Jc was above 100,000 A cm2 at 4 T and 5 K. Under the same conditions, Jc for MgB2 made from SC was slightly worse than for the MgB2 made from AB, 100,000 A cm2. On the other hand, MgB2 made from CB presented sharply reduced Jc with Ni–Co–B doping at both measured temperatures, 5 K and 20 K.