In the present research work we evaluate the in vivo distribution of gold nanoparticles (AuNPs) at different time durations after intravenous administration in mice. AuNPs with size of about 20 nm and concentration of 1 mM were synthesized by gamma irradiation method using 0.5% alginate as a stabilizer. AuNPs were characterized by UV-Vis spectrum and transmission electron microscope (TEM) image. The as-synthesized AuNPs solution was centrifuged to concentrate to 2 mg AuNPs/1 ml solution. Intravenous administration of AuNPs in mice was done at the tail with 1 mg AuNPs (0.5 ml). After 1, 3, 6 and 12 h of injection, blood was collected, mice were sacrificed and various tissues/organs were removed. The blood haematology and serum clinical chemistry indexes of mice intravenously injected with AuNPs were not significantly different compared to those of the control ones. In addition, gold content in the samples was quantitatively determined by k 0 -neutron activation analysis (k 0 -NAA) at nuclear research reactor, Da Lat Vietnam. Results showed that after 1 h of administration, AuNPs were mainly accumulated in blood (41.56%), in liver (51.60.%), in lung (6.16%) and in kidney (0.53%). After that the content of AuNPs in blood was decreased to nearly normal at 6 h while the content of AuNPs in liver, lung and kidney was accumulatively increased. After 6 h of administration AuNPs were mainly accumulated in organs like liver (76.33%), lung (11.86%) and kidney (2.23%). Thus, the obtained results are practically useful for using AuNPs as x-ray contrast agent, especially for blood and liver.