Decompositions of methyl linoleate hydroperoxide (LOOH) induced by di-t-butyl diperoxyoxalate and cobalt ions were investigated in benzene at 50 degree C under vacuum to elucidate the degradation mechanism. The major products were dimer (LOOL), oxodiene, hydroxydiene and epoxyhydroxyene (and/or epoxyoxoene). It was suggested that these products were formed by the recombination of L multiplied by (times) and LOO multiplied by (times) radicals, beta -scission of LO multiplied by (times) radical, hydrogen abstraction of LO multiplied by (times) radical, and intramolecular epoxidation of LOO multiplied by (times) radical, respectively. The decomposition of methyl linolenate hydroperoxide (L'OOH) was also studied. The major products were dimer, oxotriene, hydroxytriene, and thiobarbituric acid reactive substances, which were suggested to be formed by the intramolecular cyclization of l prime OO multiplied by (times) radical.