The present study was designed to investigate the distribution, accumulation and excretion of hydroxylapatite nanoparticles (nano-HAP) in mice with intravenous injection. The nano-HAP suspension was neutron activated and then stored 151d after neutron activation for experiment. The mice injected with radioactive nano-HAP heve sacrificed at 15min、1h、2h、4h、8h、24h、72h and the main organs were harvested for further measuring the counts of ,45,Ca in every sample by use of a liquid scintillation counter. Results indicate that ,45,Ca could be detected in all main organs (0.5~250Counts/min•mg), and there are more ,45,Ca exist in lung, liver and spleen. The counts of ,45,Ca in bone almost keep the same during the whole experiment period while counts of ,45,Ca of all other tissues decrease with time. And the counts of ,45,Ca exerted in faeces are higher than that in urine. So we can conclude that nano-HAP distribute in all organs of mice especially in lung, liver and spleen. But bone is the only tissue in which nano-HAP accumulated. Nano-HAP was excreted mostly through faeces.