A process for the preparation of tetrahydropyran-4-carboxylic acid and esters thereof of the general formula I ##STR1## in which R.sup.1 denotes hydrogen, C.sub.1 -C.sub.6 alkyl, C.sub.5 -C.sub.8 cycloalkyl, or aryl by the reaction of a dihydro-2(3H)furanone of the general formula II ##STR2## in which R.sup.2 denotes hydrogen, C.sub.1 -C.sub.6 alkyl, or --CO--R.sup.3 andR.sup.3 denotes hydrogen or C.sub.1 -C.sub.6 alkyl, with water or an alcohol of the general formula IIIR.sup.1 --OH (III),in whichR.sup.1 has the aforementioned meaning,at temperatures ranging from 200.degree. to 350.degree. C. in the presence of a heterogenous acid catalyst, in which use is made of a fixed heterogenous acid catalyst.