In order to promote the application of molybdenum (Mo) tailings in concrete industry, this paper studies the grinding characteristics of Mo tailings, the mechanical and hydration properties of mortars containing Mo tailings by X-ray diffraction (XRD), scanning electron microscope (SEM), laser particle size analysis, specific surface area analysis and strength test. The optimal grinding time is 80 mins to obtain the ground Mo tailings (-0.16 mm) with a specific surface area of 501 m2 kg-1 as mineral admixtures to the cementitious materials. With the coarse Mo tailings (+0.16 mm) as fine aggregate, composite mortars with a good workability were obtained with the compressive strength of 83.5 MPa and the flexural strength of 14.4 MPa after cured for 28 days. The comprehensive utilization rate of Mo tailings is 71 % in the composite mortars. The hydration of the cementitious composite containing Mo tailings at early age is primarily due to the hydration of the cement clinker (CC). While the large amount of quartz remains inert, the pozzolanic reaction of ground Mo tailings leads to the strength increases in long term. The main hydration phases in the cementitious composite are calcium silicate hydrates (C-S-H gels) and ettringite (AFt).