A kinetic study of the reaction between an aroxyl radical (ArO center dot) and fatty acid esters (LHs 1-5, ethyl stearate 1, ethyl oleate 2, ethyl linoleate 3, ethyl linolenate 4, and ethyl arachidonate 5) has been undertaken. The second order rate constants (k(s)) for the reaction of ArO center dot with LHs 1-5 in toluene at 25.0 degrees C have been determined spectrophotometrically. The k(s) values obtained increased in the order of LH 1 < 2 < 3 < 4 < 5, that is, with increasing the number of double bonds included in LHs 1-5. The k(s) value for LH 5 was 2.93 X 10(-3) M-1 s(-1). From the result, it has been clarified that the reaction of ArO center dot with LHs 1-5 was explained by an allylic hydrogen abstraction reaction. A similar kinetic study was performed for the reaction of ArO center dot with six carotenoids (Car-Hs 1-6, astaxanthin 1, beta-carotene 2, lycopene 3, capsanthin 4, zeaxanthin 5, and lutein 6). The k(s) values obtained increased in the order of Car-H 1 < 2 < 3 < 4 < 5 < 6. The ks value for Car-H 6 was 8.4 x 10(-4) M-1 s(-1). The ks values obtained for Car-Hs 1-6 are in the same order as that of the values for LHs 1-5. The results of detailed analyses of the ks values for the above reaction indicated that the reaction was also explained by an allylic hydrogen abstraction reaction. Furthermore, the structure-activity relationship for the reaction was discussed by taking the result of density functional theory calculation reported by Martinez and Barbosa into account.