Glioblastomas are highly vascularized tumors and anti-angiogenic strategy is one of the most promising therapeutic approaches to treat brain tumors. Interferon alpha (IFN-alpha) as a single agent or combined with standard chemo-therapy has been shown to inhibit various tumors, but the effect of combination anti-angiogenic therapy on brain tumors has not been well studied. We determined the optimal dose and schedule of pegylated IFN-alpha (PEG-IFN-alpha) against U-87MG human glioblastoma cells growing orthotopically in nude mice, since several clinical trials reported that PEG-IFN-alpha administered at higher or lower doses was less effective. The group treated two times per week with injections of 10 KU of PEG-IFN-alpha for 4 weeks showed significant decreases in cell proliferation and angiogenesis. Moreover, the optimal dose and schedule of PEG-IFN-alpha determined in this study and combined with paclitaxel treatment potently inhibited tumor growth in vivo. The mechanisms of the significant therapeutic effects were most likely caused by directly inhibiting cell proliferation and angiogenesis, and rendering apoptosis increased. Specifically PEG-IFN-alpha/paclitaxel combination induced apoptosis of tumor-associated endothelial cells more than that of tumor cells. These results suggest that optimal biological dosage and scheduling of PEG-IFN-alpha and paclitaxel combination is a potent strategy for glioblastoma patients as a new synergistic anti-endothelial treatment.