Catalysis of the formation of cyclic ethers from an unsaturated alcohol, 0-methylhept-5-en-2-ol, and of bicyclic ethers from 1,3-diols-by metal (IV) phosphates has been investigated. Good yields were obtained. The diol, 1-(2-hydroxyethyl)cyclopentanol, was cyclised to form an oxetane ring, which is the intermediate in a reverse Prins reaction and provides an alternative to reaction through a cyclic five-membered ring. The reactivity of the metal (IV) phosphate catalysts can be contrasted to that of superacidic solvent systems containing fluorosulphuric acid.