TECHNOLOGY FOCUS - BIOTECHNOLOGY - Preferred Vector: The surface expression vector of a target protein comprises a fadL gene encoding an Escherichia coli outer membrane protein (FadL), an antibiotic-resistant gene, a promoter, a gene encoding a target protein, and a gene recombinant which is constructed, to be expressed on the surface of the cell in a form fused with the FadL protein if the target protein-encoding gene is expressed in a host cell. A linker is inserted into the middle portion of the fadL gene, and the target protein-encoding gene is inserted into the linker. The C-terminal end of the fadL is truncated, and the target protein-encoding gene is inserted into the position of the truncated C-terminal end. A base sequence following the ninth loop of the fadL gene is truncated, and the target protein-encoding gene is inserted into the position of the truncated base sequence. The target protein is a protein with a portion of amino acid sequence eliminated, or a protein mutated position-specifically, to facilitate the expression of the target protein on the surface. The promoter is a trc promoter or a gntT104 promoter.Preferred Microorganism: The microorganism used for the transformation is modified such that an extracellular or intracellular protease that degrades the target protein cannot be produced to facilitate the cell surface expression of the target protein. The microorganism is bacterium. The bacterium is Escherichia coli.Preferred Method: The method for the cell surface expression of a target protein comprises culturing the transformed microorganism to express a target protein on the cell surface of the microorganisms and collecting the cells having the target protein expressed on their surface. The target protein is hormones, hormone analogues, enzymes, enzyme inhibitors, signaling proteins or their parts, antibodies or their parts, single chain antibodies, binding proteins, binding domains, peptides, antigens, adhesion proteins, structural proteins, regulatory proteins, toxin proteins, cytokines, transcriptional regulators, blood coagulation factors, and plant defense-inducing proteins. The enzyme is lipase.Preparing antibodies in vertebrate animals comprises:(a) administering the cells which are produced by the method of cell surface expression of a target protein, and have antigens expressed on their surface, to the vertebrate animals except for human beings, thereby inducing an immune response in the vertebrate animals; and(b) collecting antibodies produced by the immune response.Improving a target protein comprises:(a) constructing a mutant library of a gene encoding a target protein;(b) constructing a gene recombinant which contains the gene mutant library and a fadL gene to express the mutant of the target protein in a form fused with a FadL protein;(c) transforming a host cell with either the gene recombinant or a vector containing the gene recombinant, the host cell consisting of gram negative bacteria, gram positive bacteria, actinomyces, yeasts and molds;(d) culturing the transformed host cells to express the gene mutant library on the cell surface; and(e) screening the cells on which a target protein with improved characteristics have been expressed.The screening step is performed by using an activity of the target protein, a protein recognizing a substance labeled to the target protein, a labeled ligand binding to the target protein, or an antibody binding specifically to the target protein.