The kinetics of leaching rare earth from a manganese-removed weathered rare earth mud (MRW-RE mud) in hydrochloric acid solutions was investigated in this study as a function of temperature, particle size, and HCl concentration. It was found that the leaching process can be described by a shrinking-core model, with the apparent activation energy about 10.17 kJ/M. When the concentration of hydrochloric acid was below 4M, the RE leaching rate was controlled by the diffusion of reactants and leaching products through a porous ore. However, when HCl concentration was higher than 4 M, the leaching process was limited by both chemical reaction and reagent diffusion. Based on the experimental results, an empirical equation relating the rate constant of rare earth leaching to the particle size and leaching temperature was established for the purpose of process deign.