The coercivity of anisotropic cast–hot‐pressed Pr19Fe74.5B5Cu1.5magnets is investigated. The microstructure features and virgin magnetization curve reveal a nucleation‐controlled coercivity mechanism. Regression analysis shows that the intrinsic coercivity varies inversely as the logarithm of the average grain size:iHc(kOe) = 21.7550 − 6.0517 ln d(&mgr;m), which is in good agreement with the nucleation statistical model. Investigation of Cu addition and Nd substitution shows that Cu mainly plays a role of suppressing grain growth during the final annealing. Higher coercivity is thus obtained with Cu addition. Nd19Fe74.5B5Cu1.5magnets exhibit a much lower coercivity due to their coarse‐grained cast structure.