During tumor development, stromal cells are co-opted to the tumor milieu and provide favorable conditions for the tumor. Hypoxia stimulates cancer cells to acquire a more malignant phenotype via activation of hypoxia-inducible factor 1 (HIF-1). Given that cancer cells and astrocytes in glioblastomas coexist in a hypoxic microenvironment, we examined whether astrocytes affect the adaptation of glioblastoma cells to hypoxia. Immunoblotting, reporter assays, quantitative RT-PCR, and chromatin immunoprecipitation were performed to evaluate HIF-1 signaling in glioblastoma cells. Astrocyte-derived chemokine C-C motif ligand 20 (CCL20) was identified using cytokine arrays, and its role in glioblastoma development was evaluated in orthotopic xenografts. Astrocytes augmented HIF-1α expression in glioblastoma cells under hypoxia. The expression of HIF-1 downstream genes, cancer colony formation, and Matrigel invasion of glioblastoma cells were stimulated by conditioned medium from astrocytes pre-exposed to hypoxia. CCL20 was secreted in a hypoxia-dependent manner from astrocytes and busted the hypoxic induction of HIF-1α in glioblastoma cells. Mechanistically, the CCL20/CCR6 signaling pathway upregulates HIF-1α by stimulating nuclear factor kappa B-driven transactivation of the HIF1A gene. Compared with the control tumors, CCR6-deficient glioblastoma xenografts grew more slowly, with poor vascularization, and expressed lower levels of HIF-1α and its downstream proteins. Furthermore, CCR6 expression was correlated with HIF-1α expression in GEO and TCGA datasets from human glioblastoma tissues. These results suggest that glioblastoma cells adapt well to hypoxic stress by virtue of CCL20 derived from neighboring astrocytes.