The present invention provides a process for preparing ε-caprolactone in a purity of more than 99% by cyclizing 6-hydroxycaproic esters in the liquid phase at from 150 to 400° C. and from 1 to 1020 hPa abs., and removing and condensing the compounds which are volatile under cyclization conditions, which comprises thermally treating the remaining bottom product of the cyclization in at least one further reactor, removing and condensing volatile compounds and obtaining ε-caprolactone by distillation from the condensates.