We reported a simple approach to generate gold colloidals from HAuCl4 containing aqueous solution by synchrotron X-ray irradiation at room temperature. Gold colloidals were readily formed with reasonable yield. It was also observed that the addition of NaHCO3 tremendously modified the size and size distribution of gold nanoparticles. Our preliminary drug carrying experiment showed that thus produced gold nanopartricles could successfully carry anti-tumor drug and possess potential for drug delivery applications. (c) 2006 Elsevier B.V. All rights reserved.