Abstract: The rats, which had been adapted to flaxseed lignan (secoisolariciresinol diglusoside, SDG) for 7 d, were used as a model for non-ruminant animals. Based on the reversed-phase highperformance liquid chromatography (RP-HPLC), two experiments were conducted to study the main site of the transformation of SDG, the metabolism and absorption of lignans. Experiment Ⅰ: After SDG infusion, the concentrations of SDG, enterodiol (END) and enterolactone (ENL) in the chyme of gastrointestinal tract (GIT), feces and serum in rats with or without antibiotics were measured. Experiment Ⅱ: After the bile was collected through cannula in hepatocholedchus, the levels of lignans were analyzed. The results showed that antibiotics can significantly inhibit the transformation of SDG, it may indicate that the colon and caecum, which contain more germs in GIT, produced the most mammalian lignans, and the formations of mammalian lignans depend on the flora in GIT. SDG could be absorbed into blood circulation and its content was higher than that of END and ENL. Once the SDG and mammalian lignans were absorbed, they might undergo enterohepatic circulation.