Non-invasive imaging modalities such as computed tomography are often used for diagnosis and assessment of gastrointestinal (GI) disease status over the long-term. The physiology of the GI tract can be assessed with contrast agents. Here, we present common protein (bovine serum albumin, BSA) stabilized bismuth sulfide nanoparticles with robust X-ray attenuation. Under the optimal conditions, this agent can outline the anatomy of the mouse GI tract on 3D computed tomography imaging, with the real-time and non-invasive visualization of nanoparticle distribution and the GI tract. Moreover, the investigation on long-term toxicity and biodistribution of these nanoparticles after oral administration indicate their overall safety. This is a promising agent for GI visualization and disease diagnosis.