Aujeszky's disease (AD), also called pseudorabies, is an infectious viral disease caused by an alpha herpes virus and has domestic and wild pigs, as well as a wide range of domestic and wild animals, as the natural host. Aujeszky's disease virus (ADV) virions contain several envelope glycoproteins. Among them, glycoproteins gB, gC and gD are regarded as the major immunogenicity proteins and the antibodies induced by them can neutralize virus in vitro or in vivo. In this study, we investigated expression of these glycoproteins using the bacterial and baculovirus expressionn system. Successful expression of ADV glycoproteins in E. coli was confirmed by SDS-PAGE and Western blot analysis and their optimal expression condition was determined. However, the recombinant proteins generated in the bacterial expression system which lacks glycosylation process frequently lose their biological activity. We tried to express the ADV glycoproteins using the baculovirus expression vector system. The recombinant gB, gC and gD were detected at approximately 100, 60 and 50 kDa on SDS-PAGE and Western blotting, respectively. The optimal expression conditions were determined for MOI(multiplicity of infection) and post-infection days. One MOI and 4 or 5 days post-infection were the best conditions for the expression of the ADV glycoproteins in Sf21 cells. We are currently investigating the antigenicity of recombinant proteins using experimental animals.