OBJECTIVE： To study the effects of ivermectin on the migration and invasion of human gastric cancer cell lines BGC-823 and MGC-803 and its mechanism. METHODS： After treated with 0， 2.5， 5， 10， 20， 40 μmol/L ivermectin for 24 h， inhibitory rate of human gastric cancer cell lines BGC-823 and MGC-803 were detected by MTT assay. Effects of 5 μmol/L ivermectin and phosphate buffercontaining 0.67‰ dimethyl sulfoxide （control group） for 24 h on the migration and invasion of` gastric cancer cells BGC-823 and MGC-803 were observed by Transwell chamber invasion assay.Western blot assay was used to detect the protein expression of TGF-β1， TGF-βR， Smad2 and Smad3 in epithelial-mesenchymal transition （EMT） markers E-cadherin， N-cadherin， Vimentin， Snail and EMT transduction pathway TGF-β/smad of BGC-823 and MGC-803 cells after treated with 5， 10 μmol/L ivermectin and phosphate buffercontaining 0.67‰ dimethyl sulfoxide （control group） for 24 h. RESULTS： Ivermectin could inhibit the growth of BGC-823 and MGC-803， inhibitory rate of it was positively correlated with its concentration. Compared with control group， the number of migration and invasion BGC-823 and MGC-803 cells were decreased significantly after treated with 5 μmol/L ivermectin （P＜0.01 or P＜0.001）； the expression of E-cadherin protein was enhanced significantly in BGC-823 and MGC-803 cells after treated with 5 and 10 μmol/L ivermectin （P＜0.05 or P＜0.01 or P＜0.001）； the protein expression of N-cadherin， Vimentin， Snail， TGF-βR， Smad2 and Smad3 were decreased significantly （P＜0.05， P＜0.01 or P＜0.001）； protein expression of TGF-β1 was decreased significantly after treated with 10 μmol/L ivermectin （P＜0.05）. CONCLUSIONS： Ivermectin can significantly inhibit the migration and invasion of gastric cancer cells BGC-823 and MGC-803， and inhibiting the biological activity of EMT by reducing the expression of TGF-β/smad pathway is one of the mechanisms that inhibit the migration and invasion of gastric cancer cells.