Understanding regulating mechanisms of cerebral blood flow (CBF) is important for clinical diagnosis and biomedical researches. We demonstrate here that phase sensitive Doppler optical coherence tomography is able to measure absolute CBF in mouse visual cortex in vivo when working in the visible-light spectral range. Both temporal and spatial profile of regional CBF variations can be resolved. We further assessed the accuracy of our method by in vitro experiments, which showed great consistency between the measured values and controlled ones. Finally, we enhanced the contrast of blood vessels to generate an angiogram showing great details of mouse cortical microvasculature.