The　radiation　resistance　of　renal　cell　carcinoma　(RCC)　remains　the　primary　obstacle　to　improve　patient　survival.　This　study　aimed　to　investigate　the　effects　of　curcumin　on　the　radiosensitivity　of　RCC　cells.　Human　RCC　cell　(ACHN)　was　exposed　to　irradiation　(IR)　and/or　curcumin　treatment.　Cell　viability,　DNA　repair,　cell　cycle,　and　apoptosis,　were　evaluated　by　MTT,　immunofluoresence　staining　and　flow　cytometry.　Moreover,　ACHN　cells　were　xenografted　into　nude　mice　and　subjected　to　IR　and/or　curcumin　treatment.　The　expression　of　NF-kappa　B　signaling　related　proteins　in　ACHN　cells　and　xenografts　was　detected　by　western　blot　analysis.　The　results　showed　that　curcumin　significantly　increased　radiosensitivity　of　ACHN　cells　by　inhibiting　the　cell　proliferation　and　DNA　damage　repair,　causing　cell　cycle　arrest　at　G2/M　phase,　inducing　apoptosis　in　vitro,　and　suppressing　the　growth　of　xenografts　in　vivo.　In　addition,　curcumin　enhanced　radiosensitivity　was　through　markedly　inhibiting　IR-induced　NF-kappa　B　signaling　by　modulating　the　related　protein　expressions　including　NF-kappa　BP65,　I-kappa　B,　VEGF,　COX2,　and　Bcl-2　in　ACHN　cells,　which　was　further　strengthened　by　NF-kappa　B　inhibitor　PDTC　treatment.　Thus,　curcumin　may　confer　radiosensitivity　on　RCC　via　inhibition　of　NF-kappa　B　activation　and　its　downstream　regulars,　suggesting　the　potential　application　of　curcumin　as　an　adjuvant　in　radiotherapy　of　RCC.　(C)　2017　Published　by　Elsevier　Masson　SAS.