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The crystal structure, microstructure, and mechanical properties of HfMo_xNbTaTiZr (x≤1) alloys were investigated by X-ray diffraction, scanning electron microscopy, and compression testing. All the as-solidified HfMo_xNbTaTiZr alloys possess a simple body-centered cubic structure. Lattice parameters of the HfMo_xNbTaTiZr alloys decrease with an increase in Mo concentration, but the corresponding densities show an opposite trend. The yield strength of the HfMo_xNbTaTiZr alloys increases from 1015 MPa to 1512 MPa as x increases from 0 to 1. The solid solution strengthening is linearly proportional to a Mo concentration suggesting that the strengthening effect from each Mo atom is additive. Except for the HfMoNbTaTiZr alloy, HfMo_xNbTaTiZr (x<1) alloys exhibit excellent room-temperature plasticity (>50%). The material with x=0.75 is a new ductile refractory high-entropy alloy with promising mechanical properties.