The present study was designed to investigate the distribution, accumulation and excretion of hydroxylapatite nanoparticles (nano-HAP)in mice with intramuscular administration. Mice were injected at 91 mg/kg with either nano-HAP or hydroxylapatite microparticles (micro-HAP) activated by neutrons, and then sacrificed at 1, 2 , 4 , 8, 12, 18, 24 week for getting samples, respectively. The main organs of the experimental animals were harvested for digestion, and then the counts of 45Ca in every sample were measured by a liquid scintillation counter. The results indicated that 0–79 counts×min-1×mg-1 45Ca could be detected in all main organs after nano-HAP injection and 0–25 counts×min-1×mg-1 after micro-HAP injection. There were no significant differences between the SNP group and SMP group (p>0.05) in the distribution in vivo. Bone is the only tissue for accumulation of nano-HAP and micro-HAP. Compared with micro-HAP, a larger amount of nano-HAP accumulated in bone. The results suggest that nano-HAP have a better osseointegration and bone inductivity.Cited