The effect of ball milling on the magnetic properties of the Pr15Fe80B5alloy, whose as‐cast structure was composed of matrix phase Pr2Fe14B and Pr‐rich and &agr;‐Fe phases, has been investigated by measuringiHc, thermomagnetic curves, and x‐ray diffraction (XRD) patterns. By ball milling using a planetary ball mill up to 96 h,iHcdecreased with the amorphization of the matrix and Pr‐rich phases. However, subsequent heat treatments gave rise to the marked increase ofiHc. The alloy, after 48 h of ball milling and subsequent 600 °C annealing possessediHcof 17.4 kOe,Brof 5.8 kG, and (BH)maxof 6.5 MGOe. This alloy showed sharp diffraction peaks of Pr2Fe14B phase, while the &agr;‐Fe phase peak, which persisted through the ball milling process, almost disappeared. The highiHcof the Pr‐Fe‐B alloy, subjected to optimum milling and subsequent annealing, was attributed to a very fine Pr2Fe14B phase precipitation from the amorphous state and to the effective solution of the &agr;‐Fe phase into the matrix phase. Also, a small addition of Cu to the Pr15Fe80B5alloy was found to increase the coercivity. Further, the alloy milled for 12 h and annealed at 600 °C for 1 h showediHcof 19.7 kOe,Brof 7.0 kG, and (BH)maxof 10.2 MGOe.