In this research, we found DLL1, as a kind of Notch1 active ligand, was upregulated in DEX‐induced adipocytes compared with BMSCs, and adipocytes promoted the clonality and resistance of T‐ALL cells by activating the Notch1 signaling pathway via DLL1 and Notch1 binding. This evidence concerns the gene DLL1 and acute lymphoblastic leukemia.