Episesamin is an isomer of sesamin, resulting from the refining process of non-roasted sesame seed oil. Episesamin has two methylendioxyphenyl groups on exo and endo faces of the bicyclic skeleton. The side methylendioxyphenyl group was metabolized by cytochrome-P450. Seven metabolites of episesamin were found in rat bile after treatment with glucuronidase/arylsulfatase and were identified using NMR and MS. The seven metabolites were (7α,7'β,8α,8'α)-3,4-dihydroxy-3',4'-methylenedioxy-7,9':7',9-diepoxylignane (EC-1-1), (7α,7'β,8α,8'α)-3,4-methylenedioxy-3',4'-dihydroxy-7,9':7',9-diepoxylignane (EC-1-2) and (7α,7'β,8α,8'α)-3,4:3',4'-bis(dihydroxy)-7,9':7',9-diepoxylignane (EC-2), (7α,7'β,8α,8'α)-3-methoxy-4-hydroxy-3',4'-methylenedioxy-7,9':7',9-diepoxylignane (EC-1m-1), (7α,7'β,8α,8'α)-3,4-methylenedioxy-3'-methoxy-4'-hydroxy-7,9':7',9-diepoxylignane (EC-1m-2), (7α,7'β,8α,8'α)-3-methoxy-4-hydroxy-3',4'-dihydroxy-7,9':7',9-diepoxylignane (EC-2m-1) and (7α,7'β,8α,8'α)-3,4-dihydroxy-3'-methoxy-4'-hydroxy-7,9':7',9-diepoxylignane (EC-2m-2). EC-1-1, EC-1-2 and EC-2 were also identified as metabolites of episesamin in human liver microsomes. These results suggested that similar metabolic pathways of episesamin could be proposed in rats and humans.