The effect of a severe mechanical milling treatment on the microstructure, magnetic and magneto-caloric properties of Pr2Fe17 powders is reported. Bulk alloys showing a rhombohedral Th2Zn17-type crystal structure were mechanically ball milled under Ar atmosphere. After 10 h of milling this crystal structure persists and the mean values of the lattice parameters remain almost unchanged. Average grain sizes around 27 nm were estimated by both, transmission electron microscopy and neutron powder diffraction measurements. While for the starting bulk alloys the low field temperature of the magnetization, M(T), shows a well-defined and sharp decrease at the Curie temperature, T-c = 285(2) K, in ball milled samples the transition becomes broad not allowing an accurate determination of Curie point; in addition, this intrinsic parameter seems to be shifted toward a higher temperature [292(10)K]. The magnetocaloric effect at mu H-o(max) = 5 T was evaluated from the temperature dependence of magnetic entropy change, through the variation of M(H,T) curves. A decrease in the peak value of magnetic entropy change, vertical bar Delta S-M(max)vertical bar, from 5.7 to 3.7 J kg(-1) K-1, and the broadening of the maximum is observed for the milled sample respect to the bulk alloy. (C) 2008 Elsevier B.V. All rights reserved.