Malignant brain tumors contain a hypoxic environment rich in infiltrates of inflammatory glial cells that may influence tumor progression and T-cell function. Here, we present that hypoxia-induced glial Galectin-9 (Gal9) function as a modulator of innate immune response against tumor in a hypoxia-inducible factor (HIF)-2α-dependent manner. In vitro and in vivo, glial Gal9 highly expressed not only in hypoxic tumor region of mouse tumor model, but also in activated glia responding to tumor. Notably, expression and production of Gal9 is distinctively regulated dependent on HIF-2α, but not HIF-1α using tissue targeted mutant mice. Collectively, our data suggest that Gal9 secreted from activated glia in hypoxic tumor region and contribute to immunosuppressive environment.