To obtain sorbic acid in a good yield, while suppressing the generation of tars, by hydrolyzing a polyester with a mineral acid in the presence of a saturated fatty acid.

This method for producing sorbic acid comprises hydrolyzing a polyester having repeating units of the formula with a mineral acid (e.g. hydrochloric acid) in the presence of a saturated fatty acid (e.g. acetic acid) at 25-110°C for 15-240min. The polyester is obtained by polycondesing croton aldehyde with ketene under such a condition that the ratio of the sum of the mole number (A) of the acetic acid and the mole number (H) of water to the mole number (K) of the ketene [namely (A+H)/K] is 0.01-1.0. The saturated fatty acid is contained in a concentration of 1-20wt.% in the mineral acid. The method enables to lower a decomposition temperature for the polyester without enhancing the concentration of the mineral acid. The employment of acetic acid as the saturated fatty acid enables to repeatedly use the mineral acid mother solution, thereby being profitable. Sorbic acid is used as a food additive.