Achieving photoacoustic microscopic imaging through a miniaturized scanning head is a crucial step toward high-resolution photoacoustic endoscopy. In this work, we have developed a miniaturized probe head using a microelectromechanical systems (MEMS) based mirror for raster scan of the laser beam and our newly developed super broad bandwidth microring resonator based ultrasound detector for photoacoustic signal detection. Through this all-optical design, which offers unique advantages for endoscopic applications, this system is capable of three-dimensional (3D) imaging with high resolution of 17.5 μm in lateral direction and 20 μm in axial direction at a distance of 3.7 mm. After the performance of this system was validated through the experiments on printed grids and a resolution test target, microscopic imaging of the 3D microvasculatures in canine bladders was also conducted successfully, demonstrating the potential of novel photoacoustic endoscopic in future clinical management of bladder cancer.