It is known that uniformly dispersed rare earth oxide (RE2O3) nanoparticles in molybdenum matrix could improve the ductility of Mo. However, it is reported that the agglomeration of La2O3 was quite serious when the addition amount of La2O3 was over 2 wt%, which leaded to a dramatic decrease of the ductility of Mo. In this paper, a new type of uniformly dispersed Er2O3 doped Mo powder was prepared, with the amount of Er2O3 accounting for 4 wt%. It is found that the reduction temperature of MoO3 was higher and the grain size was smaller for the Mo powders doped with Er2O3 than those doped with La2O3. First-principles calculations illustrate that La2O3/Er2O3 had a strong trend to be absorbed on the surface of MoO3, and the inhibition capability for the reduction of MoO3 to MoO2 by Er3+ was larger than La3+ due to the stronger Er-O interactions. It gives a potential explanation of the higher reduction temperature of MoO3 doped with Er2O3 than that doped with La2O3. Furthermore, the formation energies of Er-O and La-O pairs within the bulk Mo were in the sequence: La-O > Er-O > 0 eV, indicating that these systems are unstable and La2O3 is easier to escape from the interior of Mo grains and agglomerate on the Mo surface than Er2O3. (C) 2019 Elsevier B.V. All rights reserved.