Background/Aims:　The　study　aimed　to　explore　the　effects　of　Epstein-Barr　virus-encoded　BARF1　in　human　gastric　epithelial　cells　(GES-1).　Materials　and　Methods:A　eukaryotic　expression　vector　carrying　BA　RFigene　(pcDNA3.1-BARF1)　was　constructed.　The　pcDNA3.1-BARF1　was　transfected　into　GES-1　cells,　and　they　were　selected　by　G418.　The　GES-1　cells　lines　that　expressed　BARF1　(GES-1-BARF1)　were　obtained.　The　cycle　of　GES-1-pcDNA3.1　cells　(GES-1　cells　transfected　with　empty　vector),　GES-1-BARF1　cells　(GES-1　cells　transfected　with　BARF1),　and　TPA-GES-1-BARF1(GES-1-BARFI　cells　stimulated　by　12-O-tetraclecanoylphorbol-13-acetate　(TPA)　were　analyzed　by　flow　cytometry.　Colony　formation　in　soft　agar　and　tumorigenicity　of　the　transfected　cells　in　mice　with　severe　combined　immunodeficiency　(SCID)　were　also　observed.　Results:　The　morphology　of　GES-1-BARF1　cells　were　changed　from　the　original　shuttle　to　round,　the　adhesion　between　the　cells　and　bottle　wail　was　weakened,　and　the　cells　showed　overlapping　growth.　The　proliferation　rote　of　GES-1-BARF1　and　TPA-GES-1-BARF1　cells　were　faster　than　GES-1　and　GES-1-pcDNA3.1　cells;　the　S　phase　was　significantly　prolonged　for　GES-1-BARF1　and　TPA　-GES-1-BARFI.　GES-1-BARF1　and　TPA-GES-1-BARF1　cells　formed　colonies　in　soft　agar,　with　a　cloning　rate　of　24.2%　(58/240)　and　40.0%　(96/240),　respectively;　GES-1　and　GES-1-pcDNA3.1　cells　did　not　form　colonies　in　soft　agar.　Tumors　were　formed　in　mice　with　SCID　after　injecting　TPA-GES-1-BARF1　cell　groups.　Tumor　formation　did　not　occur　in　mice　with　SCID　after　injecting　GES-1　and　GES-1-pcDNA3.1　cell　groups,　but　nodules　were　formed　in　the　mice　with　SCID　after　injecting　GES-1-BARF1　cell　groups.　Conclusion:　GES-1-BARF1　cells　malignant　transformation　was　induced　by　transfected　BARF1　gene　and　TPA　stimulation.　This　result　indicated　that　tumor　formation　not　only　require　oncogenes,　but　also　the　stimulation　of　cancer-promoting　substance.