© 2020 Elsevier B.V. For the first time, a systematic investigation into effect of Mo element concentration on the crystal lattice constant, microhardness, and reciprocating dry sliding friction and wear properties of face-centered cubic (FCC) single phase based CoCrFeNiMo high entropy alloys (HEAs) were specifically conducted in the present study. Both the lattice constant and microhardness were found to increase with the amount of Mo element. Moreover, increasing Mo element concentration in the CoCrFeNiMo HEA was beneficial into reductions of friction coefficient and its specific wear rate when sliding wear against the GCr15 steel balls in a dry condition at room temperature. Interestingly, all studied CoCrFeNiMo HEAs exhibited almost the same wear mechanisms, which strongly depended on the applied normal load during sliding wear tests. Mo element addition had a remarkable influence on the cross-sectional microstructures after sliding wear, and grain coarsening in the middle transition region was effectively retarded by increasing the amount of Mo element in the CoCrFeNiMo HEA.