Abstract TiO₂ is popular in modern industries, including dyestuffs, printing, and cosmetics. To convert titanium slag to TiO₂ with maximum efficiency, mechanical activation is an important pretreatment step to control the particle size of the titanium slag and the subsequent leaching process. Our study used a planetary high-energy ball mill to wet the titanium slag by mechanical activation for 3, 9, and 15 h to obtain the optimized condition for particle size control of the pretreated titanium slag. The phase composition was characterized by XRD, FT-IR, and Raman spectroscopy. The main constituents of the titanium slag were determined to be rutile TiO₂ and Fe₃Ti₃O₁₀. Calculating the relative intensity showed that some encapsulated phases were opened because of mechanical activation. The weight and density of titanium slag in the same volume increased, resulting in significantly enhanced peaks. The results can greatly improve the efficiency of subsequent titanium dioxide production. A laser particle size analyzer and SEM characterized the mechanical activation product. The results showed that when the mechanical activation duration is 15 h, the titanium slag obtained has a small particle size and a uniform, smaller specific surface area, and narrow particle size distribution. The current report has not introduced wet grinding to pretreat titanium slag. This simple method can be effectively applied to pre-treat titanium slag raw materials.