The microstructure and magnetic properties of bulk crystalline and ball - milled binary HoCo3 inter metallic compounds were studied. The presence of PuNi3 type of crystal phase was confirmed in all investigated specimens. The emergence of a partly amorphous phase was demonstrated at the end of grinding process. The influence of the applied high energy ball - milling parameters on the microstructure was investigated. The influence of the increased milling time on the final size of particles and crystallites was characterized by a variety of complementary measurement methods. The fabrication of nanoflakes and agglomerates for long pulverization times was demonstrated. Furthermore, the non-linear dependence of the saturation magnetization, coercivity and remanence driven by high energy ball - milling was evidenced. The enhancement of the coercivity for a low milling time was shown. A quantitative analysis of the XPS spectra over ion etching indicates the formation of Co oxides on the nanoflakes surface. (C) 2017 Elsevier B.V. All rights reserved.