13-(Z)-Retinoic acid is prepared bya) reacting 5-hydroxy-4-methyl-2(5H)-furanone with a [3-methyl-5-(2,6,6-trimethyl-1-cyclohexen-1-yl)-2,4-pentadienyl]triarylphosphonium salt andb) subsequently partially isomerizing the resulting mixture of 13-(Z)- and 11,13-di-(Z)-retinoic acid,where the reaction in step a) is carried out in the presence of lithium hydroxide as alkali metal hydroxide and in dimethylformamide as solvent at from +10.degree. to -9.degree. C. and/or the isomerization in step b) is carried out by irradiating the mixture of isomers obtained in a) in an organic solvent in the presence of a photosensitizer with light in the wavelength range from 200 to 600 nm.