Functionalized dendrimer-entrapped gold nanoparticles (Au DENPs) are of scientific and technological interest in biomedical applications. In this study, Au DENPs prepared with amine-terminated generation 5 (G5) poly(amido amine) dendrimers as templates were subjected to acetylation to neutralize the positive surface charge of the particles. By varying the molar ratio of Au salt to G5 dendrimer, we prepared acetylated Au DENPs with a size range of 2-4 nm. Meanwhile, we attempted to add glucose to the dialysis liquid of the acetylated Au DENPs to prevent possible particle aggregation after lyophilization. The acetylated Au DENPs with different compositions (Au salt/dendrimer molar ratios) were characterized with H-1-NMR, transmission electron microscopy, ultraviolet-visible (UV-vis) spectrometry, and zeta-potential measurements. We show that when the molar ratio of Au salt to dendrimer was equal to or larger than 75: 1, the acetylated Au DENPs showed a significant aggregation after lyophilization, and the addition of glucose was able to preserve the colloidal stability of the particles. X-ray absorption measurements showed that the attenuation of the acetylated Au DENPs was much higher than that of the iodine-based contrast agent at the same molar concentration of the active element (Au vs iodine). In addition, the acetylated Au DENPs enabled X-ray computed tomography (CT) imaging of mice after intravenous injection of the particles. These findings suggest a great potential for acetylated Au DENPs as a promising contrast agent for CT imaging applications. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 119: 1673-1682, 2011