Objective To analyze the characteristics of virus-like particles(VLPs)of human papilloma virus(HPV)18.Methods HPV18 VLPs were obtained by self-assembly of L1 protein expressed by recombinant E. coli expression system and analyzed for primary structure by mass spectrometry,for secondary structure by CD technique,and for tertiary and quaternary structures by high performance liquid chromatog.,transmission electronic microscopy and dynamic light scattering technique. Meanwhile,the immunogenicity of HPV18 VLPs in animals was analyzed by pseudovirusbased neutralization assay,while the purity by SDS-PAGE. Results The post-translational modification of HPV18 VLPs mainly included oxidation and deamidation,while the relative mol. mass of intact L1 monomer was about 56 000.The proportions of helix,fold,angle and irregular coil in secondary structure were 8. 4%,46. 1%,18. 5% and 30. 2%resp. The VLPs,with a purity of more than 99%,were full and intact in shape,even in size and at a diameter of about 60 nm,by which the GMT of neutralizing antibody induced in mice reached more than 3 000. However,the content of intact L1 monomer in HPV18 VLPs was more than 95%. Conclusion HPV-18 VLPs were intact in structure and even in size,which reached a high purity and showed good immunogenicity. It laid a foundation of evaluation on safety and effectiveness of cervical cancer vaccine.