Background　aims.　Mesenchymal　stromal　cells　(MSCs)　possess　the　ability　to　repair　brain　injuries.　Additionally,　nimodipine　is　a　neuroprotective　agent　that　increases　cerebral　blood　flow　and　may　help　with　the　homing　of　MSCs　to　the　injury　site.　Here　we　investigate　the　effectiveness　of　a　combined　human　umbilical　cord　derived　MSCs　and　nimodipine　therapy　in　radiation-induced　brain　injury　(RIBI).　Methods.　Female　mice　received　whole　brain　irradiation　(WBI)　and　were　treated　with　saline,　nimodipine,　hUC-MSCs,　or　hUC-MSCs　combined　with　nimodipine.　Body　weight　was　measured　weekly.　An　open　field　test　for　locomotor　activity　and　a　step-down　avoidance　test　for　learning　and　memory　function　were　conducted　at　week　4　and　week　12　post-WBI.　The　histological　damage　was　evaluated　by　hematoxylin　and　eosin　staining　and　glial　fibrillary　acidic　protein　immunohistochemistry.　Quantitative　polymerase　chain　reaction　and　Western　blotting　were　used　to　detect　apoptosis-related　mediators　(p53,　Bax　and　Bcl-2).　Results.　In　mice　receiving　the　hUC-MSCs　or　the　combined　treatment,　their　body　weight　recovered,　their　locomotor　and　cognitive　ability　improved,　and　the　percentage　of　necrotic　neurons　and　astrocytes　was　reduced.　The　combined　therapy　was　significantly　(P　＜　0.05)　more　effective　than　hUC-MSCs　alone;　these　mice　showed　decreased　expression　of　pro-apoptotic　indicators　(p53,　Bax)　and　increased　expression　of　an　anti-apoptotic　indicator　(Bcl-2),　which　may　protect　brain　cells.　Conclusions.　We　demonstrated　that　hUC-MSCs　therapy　helps　recover　body　weight　loss　and　behavior　dysfunction　in　a　mice　model　of　RIBI.　Moreover,　the　effectiveness　of　the　combined　hUC-MSCs　and　nimodipine　therapy　is　due　to　apoptosis　inhibition　and　enhancing　homing　of　MSCs　to　the　injured　brain.