It is prospective to use mammalian cells for producing fully active eukaryotic proteins. Vaccinia virus vector provides a simple, practical means for this purpose. As a vector, vaccinia virus has a number of useful characters: wide host range, non-carcinogenicity,permitting of cloning large fragments of foreign DNA (＞20 kb), retention of infectivity after insertion of foreign DNA, relatively high level of protein synthesis as well as "appropriate" transportation, secretion, processing and posttranslation modifications. In addition, the expressed proteins can prime immune system well to develope humoral and cellular immunity. Vaccine virus vector with high level expression will be or very useful in producing bioactive substances and constructing recombinant vaccines in mammalian cells.