Mo-based Tb2O3-Dy2O3 composites used as neutron absorbers in nuclear power reactor were synthesized by powder metallurgy. The comparative studies of Mo-based Tb2O3 and Mo-based Dy2O3 composites were carried out to deeply understand the phase evolution and microstructure characteristics of Mo-based Tb2O3-Dy2O3 composites. Ball milling induced terbium oxide and dysprosium oxide in the powder mixtures to be first fined, nano-crystallized, amorphized and finally dissolved into Mo matrix to form the supersaturated nanocrystalline solid solution that was driven by mechanical work, not by negative heat of mixing. Mo lattice parameter increased with increasing ball-milling time, opposite for Mo grain size. A phase transformation of Dy2O3 crystal from cubic to monoclinic and then to amorphous was observed during ball milling. The microhardness of sintered bulks was first increased and then decreased with increasing sintering time. The maximum value was obtained at the bulks sintered for 8 h. The microhardness and bulk density were increased with increasing sintering temperature before 1600 degrees C. The mechanism of ball milling and sintering was also discussed. (C) 2017 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.