3-pentenoates are prepared from 2-pentenoates by a process in which(a) a 2-pentenoate of the formula ##STR1## where R.sup.1 is alkyl of 1 to 12 carbon atoms, cycloalkyl of 5 to 8 carbon atoms, aralkyl of 7 to 10 carbon atoms or aryl of 6 to 10 carbon atoms, is reacted with a compound of the formula IIR.sup.2 -X-H IIwhere R.sup.2 has the meanings given for R.sup.1 and X is an oxygen or sulfur atom, or with a compound of the formula III ##STR2## where R.sup.3 is hydrogen or R.sup.3 and R.sup.4 are each alkyl of 1 to 12 carbon atoms, cycloakkyl of 5 to 8 carbon atoms, aralkyl of 7 to 10 carbon atoms or aryl of 6 to 10 carbon atoms, and R.sup.3 and R.sup.4 together with the nitrogen atom on which they are substituents may form a 5-membered to 7-membered ring which may additionally contain a nitrogen or oxygen atom as a hetero atom, at from 20.degree. to 300.degree. C., in the presence or absence of a basic catalyst, to give a compound of the formula IV ##STR3## where Y is --XR.sup.2 or ##STR4## in which X, R.sup.1, R.sup.2, R.sup.3 and R.sup.4 have the above meanings, and(b) the compound of the formula IV is cleaved in the liquid or gas phase in the presence of an acidic catalyst at from 150.degree. to 450.degree. C. to give a mixture of 3- and 2-pentenoates, and the 3-pentenoate is isolated.