Abstract: The valaciclovir polybutylcyanoacrylate nanoparticles (VACA-PBCA-NP) were prepared by emulsion polymerization method. The morphology, size and size distribution, release characteristics in vitro, drug loading, stability and distribution of VACV-PBCA-NP in mice were studied. The results showed that the d_av=104.77±11.78 nm, drug loading was 11.20%. The release characteristics in vitro was in accord with two-phase kinetics. 74.49% of the VACV were concentrated in liver at 15 min after iv VACA-PBCA-NP. The amount of VACV entering hepatocytes was also increased greatly. This research seems to have important value for increasing the anti-hepatitis B virus effect and decreasing toxicity of VACV.