In this study, the effects of pulsed magnetic treatment (PMT) on the microstructure and performance of pure bulk cobalt (Co) were investigated to reveal the underlying influencing mechanism of the pulsed magnetic field on ferromagnetic materials. The hardness of the material could be increased by PMT, with a maximum increase of 3.16% when 1T was adopted. The imposition of the pulsed field promoted the transformation of Co from face-centered cubic (FCC) phase to hexagonal close-packed (HCP) phase, which obeys the Shoji–Nishiyama orientation rule, with a decrease of α-Co by 8.60% and an increase of ε-Co by 0.19%. PMT also caused multiplication of defects and the formation of low-angle grain boundaries within the bulk Co. PMT could be an effective way to modify materials to suit engineering applications.