Purpose: To determine whether differences in tumor volume between arterial spin labeling (ASL) and contrast-enhanced T1-weighted MR images (CE+T1WI) can help differentiate glioblastoma (GBM) from brain metastasis. Materials and methods: Patients with a diagnosis of GBM (n=25) or brain metastasis (n=13) were examined by both conventional and ASL MR imaging. Volumes of interest with high signal intensity on ASL and CE+T1WI were defined using three dimensional analysis software. Tumor volume difference (ASL-CE) and tumor volume ratio (ASL/CE) were obtained. Absolute maximal tumor blood flow (TBF) and TBF ratio (normalized to white matter) were also measured. The Mann-Whitney U test and receiver operating characteristic curve analysis were performed to compare measurements between the tumor groups. Results: Both tumor volume difference and tumor volume ratio were significantly higher in GBM than in metastasis. Both TBF and TBF ratio were higher for GBM than for metastasis, but the differences were not significant. Conclusion: The difference in tumor volume as measured by ASL high signal intensity and CE+T1WI might be useful for differentiating GBM from metastasis, whereas ASL-derived TBF is insufficient. J. Med. Invest. 64: 58-63, February, 2017