The delineation of brain tumor margins has been a challenging objective in neurosurgery for decades. Despite the development of various preoperative imaging techniques, the current methodology is still insufficient for clinical practice. We present an intraoperative optical intrinsic signal imaging system for brain tumor surgery and establish a data processing procedure model to localize tumors. From the experimental result of a glioblastoma patient, we observe a relative small oscillation of ΔHbD in tumor region and speculate that vessels in tumor region have poor ability to provide oxygen. We applied the same data processing procedure on the second time data and proclaimed a successful surgery. Figure: Merged ΔHbD image captured prior and posterior to tumor removal.