We report a facile approach to synthesizing low generation poly(amidoamine) (PAMAM) dendrimer-stabilized gold nanoparticles (Au DSNPs) for in vivo computed tomography (CT) imaging applications. In this study, amine-terminated generation 2 PAMAM dendrimers were employed as stabilizers to form gold nanoparticles via a simple hydrothermal method. The formed aminated Au DSNPs were then acetylated to neutralize the dendrimer terminal amines, rendering the particles with improved biocompatibility. The final formed acetylated Au DSNPs were characterized via different techniques. We show that the formed Au DSNPs with an Au core size of 5.6 nm are relatively uniform and stable at different pH (5–8) and temperature (4–50 °C) conditions. X-ray attenuation coefficient measurements show that the Au DSNPs display approximately the same X-ray attenuation property as that of Omnipaque, a clinically used iodinated contrast agent. Importantly, the acetylated Au DSNPs showed much better performance in CT imaging of the major organs of rats (heart, liver, kidney, spleen, and bladder) in vivo than Omnipaque, likely due to their nanometer size and thus prolonged blood circulation time. The formed Au DSNPs may be used as a promising contrast agent for CT imaging of different biological systems.