The intestinal permeability of two flavonoid compounds liquiritin （LQ） and isoliquiritin （ILQ） was investigated using the Caco-2 cell monolayer model. In order to evaluate the permeability and predict the absorption mechanism of the two compounds, the study on bidirectional permeability from the apical （AP） side to the basolateral （BL） side as well as from the BL side to the AP side was carried out. The determination was performed by HPLC-UV method. And the permeability parameters, especially the apparent permeability coefficients （Papp）, were then calculated. The Papp values of LQ and ILQ are （5.40±0.16）× 10^-7 and （8.69±0.15）× 10^-7 cm/s, respectively. The results of time- and concentration-dependent transport experiments indicate that both LQ and ILQ are poor absorbed mainly through passive diffusion.
