Al-Ti-O inclusions always clog submerged nozzles in Ti-bearing Al-killed steel. A typical synthesized Al 2 TiO 5 inclusion was immersed in a CaO-SiO 2 -Al 2 O 3 molten slag for different durations at 1823 K. The Al 2 TiO 5 dissolution paths and mechanism were revealed by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). Decreased amounts of Ti and Al and increased amounts of Si and Ca at the dissolution boundary prove that inclusion dissolution and slag penetration simultaneously occur. SiO 2 diffuses or penetrates the inclusion more quickly than CaO, as indicated by the w(CaO)/w(SiO 2 ) value in the reaction region. A liquid product (containing 0.7-1.2 w(CaO)/w(SiO 2 ), 15wt%-20wt% Al 2 O 3 , and 5wt%-15wt% TiO 2 ) forms on the inclusion surface when Al 2 TiO 5 is dissolved in the slag. Al 2 TiO 5 initially dissolves faster than the diffusion rate of the liquid product toward the bulk slag. With increasing reaction time, the boundary reaches its largest distance, the Al 2 TiO 5 dissolution rate equals the liquid product diffusion rate, and the dissolution process remains stable until the inclusion is completely dissolved.