A high yield purification method was developed for multi- and single-walled carbon nanotubes, combining both the gas-phase purification using H2S and O2 mixture to remove impurity carbon particles and the acid treatment to remove metal particles. For the purification of MWNTs, the purification yield was about 54%, much higher than the yield previously reported. For the SWNTs, the combined liquid-gas purification process resulted in a high purity of >95% and a high yield of 20-50%, depending on the quality of raw material. Hydrogen sulfide played a role of enhancing the removal of carbon particles as well as suppressing the oxidation of carbon nanotubes. Overall, the purification method developed in this work is simple and quite effective for removing unwanted carbon and metal particles out of MWNTs and SWNTs.