ηc physics at BES III

An introduction for ηc physics research is presented in this paper, which shows that the mechanism of ηc decays can't be well described by current theoretical models and detailed experimental measurements need to be done with larger ηc sample. Based on the expected J/ψ and ψ' events taken with the planed BES III detector in one year, the ηc physics researches are discussed extensively, including the measurements of branching fractions of different final states, the search for new decay modes, precision measurements of mass and width, and the search for rare decays. At last, the study of η'c decays is also discussed briefly