A black weathering mud containing rare earth in Southwest China contains about 3%～7% RE2O3. RE in the weathering mud mainly exists on the amorphous Mn-Fe oxide, which can not be enriched by physical beneficiation methods such as floatation, magnetic and electrostatic separation or gravity concentration etc, and can not also be exchanged by salts. Chlorinating roasting is selected to treat the black weathering mud based on the thermodynamic analysis and the properties of mud in the paper. The chlorinating roasting treatment is divided two stages. The first step is to heat the mud mixed NH4Cl and carbon with (1.5～2.5)∶10 of NH4Cl/mud ratio at 200℃ for 1 h. NH4Cl directly chlorinates the RE2O3 in the weathering mud, but do not destroy Mn-Fe amorphous structure. The secondary stage is to heat the mixture to above 350℃, NH4Cl decomposes to NH3 and HCl, and carbon in the mixture also takes part in chlorinating of RE. Recovery of RE reaches to 91.6% under the conditions of temperature 450℃ and roasting for 2 h, and Pb and Mn can be further recovered at the same time.