<p>Molybdenum tailings are the solid waste left from ore processing, which damages soil and water resources. To address that, molybdenum tailings (MTs) powder obtained from molybdenum tailings sands was processed as an admixture. Compared with moisture-cured conditions, the influence of MTs on the steam-cured mortar’s mechanical properties, surface and internal pore characteristics, and microscopic morphology was investigated. The results show that steam-cured mortar containing appropriate MTs can still have high early strength. When the content of MTs doesn’t exceed 15%, the mechanical strength of mortar steam-cured for 3 d can reach 85% of that of corresponding mortar moisture-cured for 28 d, and that of mortar steam-cured for 28 d isn’t lower than 90% of that of pure cement mortar. The proportion of harmful pores (HFP) and more harmful pores (MHFP) and most probable pore diameters (MPD) on the mortar surface containing MTs steam-cured for 28 d are significantly decreased. When MTs’ content is 15%, the proportion of HFP and MHFP on the surface of paste is decreased by 71.4% and 72.2%, respectively, with MPS decreasing from 12.7 nm to 10.8 nm. SEM analysis shows that the surfaces of steam-cured paste containing 15% MTs have more hydration products and dense microstructures. The effect of pozzolanic and dense filling of MTs effectively refines the pore structure, reducing the large pore-size pores.</p>