The official methods for ‘readily oxidizable substances (ROS)’ in propionic acid as a food additive were compared. The methods examined were those adopted in theCompendium of Food Additive Specifications (CFAS)by the Joint FAO‐WHO Expert Committee on Food Additives, FAO,The Japanese Standards for Food Additives (JSFA)by the Ministry of Health and Welfare, Japan, and theFood Chemicals Codex (FCC)by the National Research Council, USA. The methods given inCFASandJSFAare the same (potassium permanganate consumption). However, by this method, manganese(VII) in potassium permanganate was readily reduced to colourless manganese(II) with some substances contained in the propionic acid before reacting with aldehydes, which are generally considered as ‘readily oxidizable substances’, to form brown manganese(IV) oxide. The FCC method (bromine consumption) for ‘ROS’ could be recommended because it was able to obtain quantitative results of ‘ROS’, including aldehydes.