The oxidation of propane-1,3- and butane-1,4-diols by quinquevalent vanadium ion has been studied in the presence of sulphuric and perchloric acids. The reaction, which is acid-catalysed, depends on the activity of water for the entire range of acid concentration used. The tentative reactive vanadium(V) species is discussed, and the experimental evidence in support of an acyclic mechanism of oxidation has been put forward.