Photoacoustic imaging is a noninvasive, nonionizing imaging modality that combines the merits of high optical contrast, good ultrasonic resolution and satisfactory imaging depth. These features make it suitable for detecting the pathological changes of subcutaneous vasculature. A setup of photoacoustic imaging system was employed to achieve images of subcutaneous vasculature and subcutaneous tumor-related vascular anomalies in mice in vivo. The networks of subcutaneous vasculature are clearly identified in the photoacoustic images, blood vessels which are invisible to the naked eye under the skin surface and tumor-related abnormal vasculature are also revealed by the photoacoustic system. Moreover, micro blood vessels correlated with the high frequency signals become evident after digital image processing based on high-pass filtering. This work demonstrates that photoacoustic imaging could potentially provide a valuable tool for monitoring the pathological changes of subcutaneous vasculature in early stage.