Ischemic stroke is currently treated with thrombolytic therapy with a drawback to induce hemorrhagic transformation (HT) if applied beyond its relatively narrow treatment time window. The present study was designed to examine the role of IMM-H004, a derivative of coumarin, in recombinant tissue plasminogen activator (tPA)-induced HT. Rats subjected to 6 h of thromboembolic occlusion or middle cerebral artery occlusion received tPA with or without IMM-H004. Delayed tPA intervention drastically increased the risk of HT and exaggerated the ischemic injury. To assess the effect of IMM-H004 on delayed treatment of tPA-induced toxicity after ischemia and reperfusion, various approaches were used, including a behavior test, TTC-staining, determination of cerebral hemorrhage, laser speckle imaging, Western blot, gelatin zymogram, immunohistochemistry and immunofluorescence staining. Experiments were also conducted in vitro in human brain microvascular endothelial cells (HBMECs) and PC12 cells to explore the mechanism for the role of IMM-H004. Combination therapy of tPA and IMM-H004 prevented the development of HT, and reduced the mortality rate, infarct volume and brain edema. IMM-H004 also exerted a protective role by decreasing matrix metalloproteinases, the co-localization of matrix metalloproteinase-2 with astrocytes and increasing occludin. Experiments in HBMECs and PC12 revealed an elevation in ATP level and a protein kinase A- and PI3K-dependent activation of Akt by IMM-H004 after tPA administration. These results suggest IMM-H004 as a promising adjuvant to alleviate the detrimental side effects of tPA in clinical therapy of ischemic stroke, and contribute to better understand the mechanism for the beneficial role of this novel remedy.