Glioblastoma (GBM) is an aggressive malignant brain tumor with median survival of 12 months and 5-year survival rate less than 5%. GBM is highly vascularized， and the interactions between tumor and endothelial cells play an important role in driving tumor growth. To study tumor-endothelial interactions， the gold standard co-culture model is transwell culture， which fails to recapitulate the biochemical or physical cues found in tumor niche. Recently， we reported the development of poly(ethylene-glycol)-based hydrogels as 3D niche that supported GBM proliferation and invasion. To further mimic the microanatomical architecture of tumor-endothelial interactions in vivo， here we developed a hydrogel-based co-culture model that mimics the spatial organization of tumor and endothelial cells. To increase the physiological relevance， patient-derived GBM cells and mouse brain endothelial cells were used as model cell types. Using hydrolytically-degradable alginate fibers as porogens， endothelial cells were deployed and patterned into vessel-like structures in 3D hydrogels with high cell viability and retention of endothelial phenotype. Co-culture led to a significant increase in GBM cell proliferation and decrease in endothelial cell expression of cell adhesion proteins. In summary， we have developed a novel 3D co-culture model that mimics the in vivo spatial organization of brain tumor and endothelial cells. Such model may provide a valuable tool for future mechanistic studies to elucidate the effects of tumor-endothelial interactions on tumor progression in a more physiologically-relevant manner.