The dissolution process of CaO·2Al2O3 (CA2) particles in CaO-SiO2-Al2O3 steelmaking slags was in situ investigated at 1550 °C. To better understand the role of particle porosity in dissolution kinetics, the particles with two different porosity levels, i.e., 0.08 and 0.20 were used in this study. The porosity (φ) and surface area of CA2 particles were characterized through X-ray Computed Tomographic Imaging (XCT), and the surface area ratio (f(φ)) between the porous and full dense particles was expressed as f(φ)=0.9398e5.9498φ. The obtained results indicated that an increase in the porosity from 0.08 to 0.20 led to an increase in the average dissolution rate from 0.35 to 0.59 μm/s. Moreover, the motion of CA2 particles during the dissolution process was observed, suggesting its importance to include in the modeling approach. A novel mathematical model was developed to predict the dissolution time of inclusion particles by incorporating both the motion and porosity of particles. This model was validated against the existing literature data and aligned well with the current experimental findings. The model predictions demonstrated that the dissolution time of CA2 particles was decreased with an increase in the velocity and porosity of particles and concentration difference of dissolving species between particle–slag interface and molten slag (∆C), and a decrease in slag viscosity.