The strong hydrophilic properties of both sub-bituminous coal and kaolinite make it difficult to separate by direct flotation. In this paper, the removal of kaolinite from fine sub-bituminous coal was investigated by reverse flotation tests using N, N-dimethyl dodecyl amine (DRN12) as a kaolinite collector. In addition, the adsorption behavior of DRN12 on coal and kaolinite surfaces was also studied to explore its interaction mechanism The experimental results showed that the beneficiation of kaolinite from the raw coal was effective only in the acid pulp with DRN12 less than 1.5kg/t. Moreover, in acid solutions, DRN12 preferentially adsorbs on kaolinite surface by electrostatic force, and the adsorption capacity of DRN12 on kaolinite surface was much higher than on coal, which caused an increase of kaolinite hydrophobicity and floatability.