Although IFNγ is regarded as a key cytokine in angiostatic response, our poor understanding of its effective cellular target drastically limits its clinical trials against angiogenesis‐related disorders. Here, we investigated the effect of IFNγ on endothelial cells (ECs) and possible molecular mechanisms in angiostasis. By employing Tie2^IFNγR mice, in which IFNγR expression was reconstituted under the control of Tie2 promoter in IFNγR‐deficient mice, we found that the response of ECs to IFNγ was highly effective in inhibiting blood supply and retarding tumour growth. Interestingly, the expression of IFNγR on Tie2⁻ cells did not inhibit, but promoted tumour growth in control wild‐type mice. Mechanism studies showed that IFNγ reacting on ECs down‐regulated the delta‐like ligand 4 (Dll4)/Notch signalling pathway. Accordingly, overexpression of Dll4 in human ECs diminished the effect of IFNγ on ECs. This study demonstrates that the action of IFNγ on ECs, but not other cells, is highly effective for tumour angiostasis, which involves down‐regulating Dll4. It provides insights for EC‐targeted angiostatic therapy in treating angiogenesis‐associated disorders in the clinic. Copyright © 2014 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.