A mixture containing hydrogen iodide and water and having a water content of not more than 5% by weight (particularly not more than 3% by weight) in a distillation system is distilled to prevent condensation of hydrogen iodide in the distillation system. The mixture may comprise hydrogen iodide, water, methanol, methyl iodide, acetic acid, and methyl acetate. Even when the mixture contains hydrogen iodide at a concentration of 1 to 3000 ppm on the basis of weight, an acetic acid product having a concentration of hydrogen iodide of not more than 50 ppm can be obtained by withdrawing a fraction containing hydrogen iodide from the top of the column, and withdrawing acetic acid as a side-cut stream or a stream from the bottom of the column. Such a process (distillation process) effectively inhibits condensation of hydrogen iodide in the distillation system and corrosion in the distillation system.