In order to promote the industrial application of the magnesiation roasting–acid leaching method, the acidic leaching kinetics of vanadium from magnesiation-roasted vanadium slag was investigated. By combination of XRD, XPS, and SEM, it was revealed that MgSiO₃ and most vanadates consumed acid sharply to produce SiO₂ and V(V)-containing vanadyl in the initial 10 min. The variation of vanadium extraction efficiency with leaching time was studied to establish the kinetic models for leaching. Results indicated two distinct stages in the leaching process and the kinetics of both stages followed the shrinking core model. The leaching rate in 0-10 min was controlled by both solid product layer diffusion and chemical reactions, while the leaching rate in 10-30 min was controlled only by chemical reactions. Therefore, it is essential to accelerate the mass transfer in initial 10 min and accurately control the temperature in the following 20 min during leaching.