Effect of grain size on formation of magnetically hard SmCo5 type precipitates in Sm-2(Co,Cu,Fe,Zr)(17) alloy when subjected to different aging conditions has been investigated and correlated with the resultant hard magnetic properties. The variation in grain size of the sintered samples was obtained by changing the milling time (3, 4 and 5 h) of the precursor alloy. The microstructural investigation and magnetic characteristics of the aged samples indicate that the intrinsic coercivity is strongly influenced by volume fraction of the SmCo5 precipitates, whereas, the knee field predominantly depends on the fineness and distribution of SmCo5 precipitates rather than its volume fraction. The fine grain sample, owing to higher fraction of grain boundaries, displays considerably larger fraction of magnetically soft precipitate free zone (PFZ) adjacent to grain boundary resulting in lower coercivity. (C) 2016 Elsevier B.V. All rights reserved.