The effect of calcium element in ferrosilicon alloys on inclusions in an Al-killed steel was studied through laboratory experiments, observation, and thermodynamic calculation. The total calcium (T.Ca) content in the molten steel increased after the addition of the ferrosilicon alloy, modifying Al2O3 and MgO·Al2O3 inclusions into CaO-Al2O3 type ones. The size of inclusions in the molten steel decreased with the increase of the CaO content in inclusions. Large size CaO-Al2O3 type inclusions were little generated. With the increase of the T.Ca in the molten steel, the T.O in the steel increased while the average size of inclusions decreased. It was indicated that the calcium element in ferrosilicon alloys had little influence on the formation of large size CaO-Al2O3 inclusions in the steel. However, the generated small solid CaO-Al2O3 type inclusions were able to clog at the wall of the submerged entry nozzle, and the subsequent dislodgement of the big clogging lump into the molten steel was one of the reasons for the existence of large and irregular shape CaO-Al2O3 type inclusions in the steel product.