The authors report the development of a head-mounted photoacoustic fiberscope for imaging cerebral oxygenation and hemodynamics in freely behaving mice. The 4.5-gram imaging probe has a lateral resolution of 9 μm and a frame rate of 0.2 Hz over a 1.2 mm wide area. The probe can continuously monitor cerebral oxygenation and hemodynamic responses at single-vessel resolution, showing significant differences in cerebrovascular responses to external stimuli under anesthesia and in freely moving states. For example, high-concentration CO₂ respiration induces enhanced oxygenation to compensate for hypercapnia, which is more pronounced in freely moving mice compared to anesthetized mice. Comparative studies with obese rodents show significantly weaker compensation capabilities. This new imaging modality is promising for investigating both normal and pathological cerebrovascular functions and studying cerebral activity, disorders, and treatments. The fiberscope's advantages include high spatiotemporal resolution, lightweight design, and the ability to visualize oxygenation and hemodynamics in freely moving animals.The authors report the development of a head-mounted photoacoustic fiberscope for imaging cerebral oxygenation and hemodynamics in freely behaving mice. The 4.5-gram imaging probe has a lateral resolution of 9 μm and a frame rate of 0.2 Hz over a 1.2 mm wide area. The probe can continuously monitor cerebral oxygenation and hemodynamic responses at single-vessel resolution, showing significant differences in cerebrovascular responses to external stimuli under anesthesia and in freely moving states. For example, high-concentration CO₂ respiration induces enhanced oxygenation to compensate for hypercapnia, which is more pronounced in freely moving mice compared to anesthetized mice. Comparative studies with obese rodents show significantly weaker compensation capabilities. This new imaging modality is promising for investigating both normal and pathological cerebrovascular functions and studying cerebral activity, disorders, and treatments. The fiberscope's advantages include high spatiotemporal resolution, lightweight design, and the ability to visualize oxygenation and hemodynamics in freely moving animals.