The cleavage products formed by the autoxidation of phytofluene were evaluated in order to elucidate possible oxidation products of phytofluene in the oxidative condition. Among a number of oxidation products formed, the following five in the carbonyl compound fraction were identified: 6, 10, 14-trimethylpentadeca-3,5,9,13-tetraen-2-one, phytapentaenal, 5,9,13,17-tetramethyloctadeca-2,4,6,8,12,16-hexaenal, 5,9,13,17-tetramethyloctadeca-2,4,8,12, 16-pentaenal, 2,7,11,15,19-pentamethylicosa-2,4,6,10,14,18-hexaenal and 4,9,13,17,21-pentamethyldocosa-2,4,6,8,12,16,20-heptaenal. In addition, 4,5-didehydrogeranyl geranoic acid was formed by the autoxidation of phytofluene in liposomal suspension. The pig liver homogenate was able to convert phytapentaenal to 4,5-didehydrogeranyl geranoic acid, in a manner comparable to the conversion of all-trans-retinal to all-trans-retinoic acid. These results suggest firstly that phytofluene is cleaved into a series of long-chain and short-chain carbonyl compounds under the oxidative condition in vitro and secondly that phytapentaenal is further enzymatically converted to 4,5-didehydrogeranyl geranoic acid.