Abstract: Method for preparing sorbic acid comprising the steps of uniformly dispersing the polyester, prepared by the reaction of crotonaldehyde with ketene, and hydrochloric acid into a saturated aliphatic hydrocarbon having a boiling point at atmospheric pressure of 150.degree. to 260.degree.C., heating the dispersed reaction mixture at 80.degree. to 135.degree.C. to convert the polyester to sorbic acid, separating the resulting reaction mixture into two layers, evaporating sorbic acid together with hydrocarbon from the upper layer by centrifugal thin film type evaporator under conditions of 20 to 40 mmHg in absolute pressure and of 140.degree. to 160.degree.C., and recovering sorbic acid from the evaporated sorbic acid-hydrocarbon mixture. Sorbic acid of high quality can be obtained in high yield.