Abstract: OBJECTIVE To study the intestinal absorption site, process and transport mechanism of the flavonoid lipid-lowering extract from Daidai fruit. METHODS Rat in situ single-pass intestinal perfusion model was used, with active parts neohesperidin and naringin as index, rutin as internal standard. Quantitative analysis method of the flavonoid lipid-lowering extract from Daidai fruit intestinal perfusate was established by UPLC-MS/MS. The extract absorption process and characteristics of different intestine segments were observed. P-gp efflux pumps inhibitor verapamil(VP) was added. The effect of P-gp on the absorption of the extract, and the changes in intestinal absorption parameters(apparent absorption coefficient P_app, absorption rate constant K_a, and percentage of accumulative absorption P%) were evaluated. The absorption and transfer process of the active parts were explored using extract samples at different concentration levels. RESULTS The flavonoid lipid-lowering extract from Daidai fruit was absorbed in the following order:duodenum>colon>jejunum≈ileum. Compared with duodenum, the absorption parameters(P_app, K_a, and P%) of neohesperidin and naringin at all the other intestine segments had significant difference(P<0.05). The P% values of neohesperidin and naringin at duodenum was about 5-7 times of those at the other intestine segments. After adding VP, the P_app, K_a, and P% values of the active parts of the extract(neohesperidin and naringin) significantly increased. The amount absorbed at duodenum also showed a significant improvement, with P% value being 4 times of VP blank group. For extracts at all three concentration levels(high, middle, and low), there was no significant changes in the P_app and K_a values of naringin. For extracts at middle and low concentration levels, the P_app and K_a values of neohesperidin increased slowly as the concentration level of the samples increases. For extracts at middle concentration level, the P_app and K_a values of neohesperidin was larger than those for the extracts at high concentration level. The difference in P_app values had statistical significance(P<0.05). CONCLUSION The main absorption site of the flavonoid lipid-lowering extract from Daidai fruit is duodenum. P-gp have significant effects on the intestinal absorption of the active parts of the extract. Both active parts show similar changes for their absorption parameters, which implies that on P-gp efflux pathway, neohesperidin and naringin do not have competitive or non-competitive inhibitory effect on each other. Under low concentration, their apparent absorption at intestine follows the first order kinetics. The absorption mechanism of naringin is probably passive transport, and the neohesperidin is probably facilitated diffusion by vector-mediation.