Using the Ames/Salmonella/microsome assay, we examined the antimutagenic effect of the hexane extract of Armeniacae semen (apricot (Prunus armeniaca L.) seed), Persicae semen (peach (P. persica Bat.) seed), and seeds of cherry (P. avium L.), plum (P. salicina Lindle) and almond (P. dulcis Mill). Hexane extracts of Armeniacae semen and Persicae semen inhibited the mutagenicity of benzo[a]pyrene (B[a]P), but those of seeds of cherry, plum and almond did not. The mutagenicities of 3-amino-1,4-dimethyl-5H-pyrido[4,3-b]indole (Trp-P-1) and 2-(2-furyl)-3-(5-nitro-2-furyl)acrylamide (AF-2) were also inhibited by the extracts of Armeniacae semen and Persicae semen. Inhibitory substances in Persicae semen were fractionated by silica gel column chromatography and high performance liquid chromatography, and were identified as oleic acid and linoleic acid. The contents of oleic acid and linoleic acid were 0.7 and 0.4% in the hexane extract of Armeniacae semen, and 1.5 and 0.5% in that of Persicae semen, respectively.