PURPOSE: To improve the quality of acetic acid economically, in an industrial scale, with single procedure, by treating a crude acetic acid with an ozone-containing gas.

CONSTITUTION: A high quality acetic acid having long color retention time by KMnO4 test and low ApHA value by H2SO4 test, is prepared by introducing an ozone-containing gas into acetic acid to be purified. The process can be applied to any acetic acid produced by industrial processes, however, it is not desirable to apply to a crude acetic acid containing too much impurities, because it consumes a large amount of the ozone-containing gas. It is most preferably applied to acetic acid having a purity of ≥99%, e.g. prepared by distilling the above crude acetic acid. The ozone-containing gas is prepared by ozonizing air or oxygen with a commercial ozonizer. Since the purification process of this invention can be carried out at room temperature under atmospheric pressure without using a distillation process, the heat energy is saved. As the post-treatment of the product is not necessary, there is no trouble of environmental pollution or safety. The process can be easily made continuous and automatic.