Olefinically unsaturated carboxylic esters having a terminal ester group and of the general formulae Ia and IbR.sup.1 --CH.sub.2 --CH.dbd.CH--(CH.sub.2).sub.r--1 --COOR.sup.2 (Ia)R.sup.1 --CH.dbd.CH--(CH.sub.2).sub.r --COOR.sup.2 (Ib)and, if desired, further double bond isomers, where R.sup.1 is hydrogen or an organic radical, R.sup.2 is C.sub.1 -C.sub.8 -alkyl and r is from 1 to 20, are prepared by a process in which an .alpha.-substituted .alpha.,.omega.-(n-alkylenedicarboxylic ester) of the general formula II ##STR1## where R.sup.1 and R.sup.2 and r have the abovementioned meanings and R.sup.3 is C.sub.1 -C.sub.8 -alkyl, is converted over an acidic heterogeneous catalyst at from 150.degree. to 800.degree. C. and under from 0.01 to 50 bar.