Mechanical grinding and subsequent annealing were applied to the $Nd_5Pr_7Fe_{82}B_6$ and $Nd_{12}Fe_{82}B_6$ ingots, and the crystal structure and magnetic properties were investigated. After 330 hours milling, the particles with $2~3mu extrm{m}$average size were identified to be composed of very fine crystallites judging from the x-ray diffraction patterns. The intrinsic coercivity of 18.36 ~ 18.79 kOe and the maximum energy product of 8.32-8.38 MGOe were obtained by the annealing of the milled powders at $600^{circ}C$ for 2 hours. Annealing at a higher temperature resulted in the improved magnetic properties. However it was revealed that the control of the micro-crystallites formed during the grinding process was more important to get an optimized magnetic properties than the annealing condition.