Increased　ubiquitin-specific　protease　22　(USP22)　has　been　associated　with　poor　prognosis　in　several　cancers　including　gastric　cancer.　However,　the　role　of　USP22　in　gastric　tumorigenesis　is　still　unclear.　Gastric　cancer　stem　cells　have　been　identified　and　shown　to　correlate　with　gastric　cancer　initiation　and　metastasis.　In　this　study,　we　found　that　silencing　of　USP22　inhibited　proliferation　of　gastric　cancer　cells　and　suppressed　the　cancer　stem　cell　spheroid　formation　in　serum-free　culture.　Furthermore,　cancer　stem　cell　markers,　such　as　CD133,　SOX2,　OCT4　and　NANOG　were　down-regulated.　Additionally,　knockdown　of　USP22　inhibited　gastric　cancer　xenografts　growth.　Our　analysis　of　TCGA　database　indicated　that　BMI1　overexpression　may　predict　gastric　cancer　patient　survival,　and　TAT-BMI1　proteins　reversed　the　USP22　knockdown-mediated　decreased　in　cancer　stem　cell　properties,　and　elevated　the　expression　of　stemness-associated　genes.　Furthermore,　we　found　that　overexpression　of　USP22　stabilized　the　BMI1　protein　in　gastric　cancer　cells.　Taken　together,　our　study　demonstrates　that　USP22　is　indispensable　for　gastric　cancer　stem　cell　self-renewal　through　stabilization　of　BMI1.　These　results　may　provide　novel　approaches　to　the　theranostics　of　gastric　cancer　in　the　near　future.