ObjectiveTo study the effect of serum containing Sanwubai San on TGF-β₁ induced epithelial mesenchymal transition （EMT） of human gastric cancer SGC-7901 cells and its mechanism in vitro based on transforming growth factor-β/Smad（TGF-β/Smad）signaling pathway. MethodTwenty-eight male SD rats （SPF grade， three months） were randomly divided into blank group and Sanwubai low （0.031 25 g·kg^-1·d^-1， ig）， medium （0.062 5 g·kg^-1·d^-1， ig） and high （0.125 g·kg^-1·d^-1， ig） dose groups， seven in each group. The blank group was given the same volume of ultrapure water （ig）. The gavage was performed once a day for seven consecutive days. The serum containing the drug was taken from the abdominal aorta 45 min after the last administration. Cell counting kit-8 （CCK-8） method was used to detect the effect of serum in Sanwubai San high dose group on the activity of SGC-7901 cells. Changes of cell morphology after treatment with TGF-β₁ and serum containing Sanwubai San were observed by microscopy， and the migration rate and invasion rate of the SGC-7901 cells were detected by cell scratch assay and transwell assay， respectively. Western blot was used to detect the expression of E-cadherin， snail， TGF-β₁， Smad3， p-Smad3 and Smad7 proteins. ResultCompared with the blank group， 10%， 15% and 20% high-dose Sanwubai San inhibited the activity of SGC-7901 cells in a concentration and time dependent manner. Compared with the conditions in the blank group， the cells in the model group lost spindle shape， and most cells became round and long. Compared with the model group， the Sanwubai San groups had decreased pseudopodia and small cells with the morphology returning to normal. Compared with the conditions in the blank group， enhanced ability of cell migration and invasion （P<0.01）， lowered expression of E-cadherin and Smad7 （P<0.01）， and increased expression of Snail， p-Smad3 and TGF-β₁ （P<0.01） were found in the model group， with the total protein level of Smad3 remaining unchanged. Compared with the conditions in the model group， the cell migration ability was inhibited in the Sanwubai San high and medium dose groups （P<0.01） after 24 h， and the ability was inhibited in all three Sanwubai San groups after 48 h （P<0.01）， while the invasion ability was enhanced. In addition， the Sanwubai San high and medium dose groups had elevated expression of E-cadherin （P<0.01） and Smad7 （P<0.01）， and decreased expression of Snail （P<0.01）， and the expression of TGF-β₁ and p-Smad3 was down-regulated in the three Sanwubai San groups （P<0.01）. ConclusionSanwubai San could inhibit TGF-β₁ induced EMT in SGC-7901 cells， and its mechanism might be related to the regulation of TGF-β/Smad signaling pathway.