To study the transportation of Xiaochaihu Tang in Caco-2 cell model. The safety concentration of Xiaochaihu Tang in Caco-2 cells was determined by MTT assay. Then the Caco-2 cell model was used to investigate the bi-directional transportation of Xiaochaihu Tang. The multicomponents of Xiaochaihu Tang and the influence of time were measured by high performance liquid chromatography (HPLC). The P(app) values of wogonoside and wogonin were (1.23 +/- 0.09) x 10(-6), (1.07 +/- 0.89) x 10(-5) cm x s(-1) from the AP side to BL side, and (2.12 +/- 0.19) x 10(-6) and (7.12 +/- 1.02) x 10(-6) cm x s(-1) from the BL side to AP side, respectively. The P(appAP --> BL)/P(app BL --> AP) ratio of wogonoside and wogonin were 0.58 and 1.49, respectively. Baicalin, baicalein and glycyrrhizic acid could not permeate the Caco-2 cell model. The transportation of wogonoside and wogonin in Caco-2 cell model may be a passive transportation.