Colorectal cancer is the second most common malignancy diagnosed globally and the 4th leading cause of cancer mortality. Critical gaps exist in diagnostic and surveillance imaging modalities for colorectal neoplasia. We have conducted a pilot study using a real-time co-registered photoacoustic (PAT) and ultrasound (US) tomography system. A total of 23 ex vivo human colorectal tissue samples (19 colon and 4 rectum) were imaged immediately after surgical resection. These results indicate potential of using PAT/US for future cancer screening and post-treatment surveillance of colon and rectum. The image resolution of the current system is low (∼ 250 μm axial resolution) due to the commercial endo-cavity ultrasound transducer array (6 MHz central frequency, 80% bandwidth). To solve the problem of image resolution, we decoded the pin configuration of a high-frequency transducer array (15 MHz central frequency, 9-18 MHz bandwidth) and adapted it to our home-made 128 channels ultrasound pulsing and receiving system to perform high-frequency PAT/US imaging. We achieved a lateral resolution of ∼ 150 μm and axial resolution of ∼ 120 μm. We also imaged a post-treated human rectum sample to evaluate the system performance.