Background:　Carfilzomib　is　a　second-generation　proteasome　inhibitor.　Lately,　it　is　approved　for　clinical　treatment　of　multiple　myeloma.　However,　its　anti-tumor　activity　and　mechanism　against　solid　tumors　has　not　been　elucidated.　The　study　is　aimed　to　investigate　the　function　and　the　mechanism　of　Carfilzomib　against　breast　cancer　cells.　Methods:　Breast　cancer　cell　line　ZR-75-30　was　treated　by　different　concentrations　of　Carfilzomib.　MTT　assay　was　used　to　examine　cell　viability.　Colony　formation　assay　was　performed　to　detect　cell　proliferation.　Flow　cytometry　was　used　to　analyze　cell　cycle　and　apoptosis,　and　Hoechst　33258　staining　was　additionally　used　to　observe　cell　apoptosis.　Western　blot　was　used　to　detect　cell　cycle-and　apoptosis-associated　protein　expression　level.　Results:　Carfilzomib　impaired　viability　and　colony　formation　ability　of　ZR-75-30　breast　cancer　cell　line　in　a　dose-dependent　manner.　Carfilzomib　treatment　suppressed　protein　expression　of　G2/M　checkpoint-specific　cyclin-dependent　kinase　CDK1　(P＜0.05)　and　CDK2　(P＞0.05).　The　pro-apoptotic　protein　Bax　was　increased,　while　the　anti-apoptotic　proteins　Bcl-2　and　Mcl-1　were　decreased　in　Carfilzomib-treated　cells　in　a　dose-dependent　manner.　Conclusion:　Carfilzomib　could　inhibit　breast　cancer　cells　proliferation　and　induce　cell　apoptosis,　indicating　its　potential　use　for　clinical　management　of　breast　cancer.