The present invention provides a method of producing a recombinant antibody efficiently and at low cost. Disclosed is a method of producing an antibody or a fragment thereof, comprising allowing a cell to produce the antibody or the fragment, wherein the cell contains a larger number of copies of an exogenous DNA encoding the light chain or a fragment thereof of the antibody than the number of copies contained in the cell of an exogenous DNA encoding the heavy chain or a fragment thereof of the antibody. The present invention also provides a recombinant vector comprising one copy of a DNA encoding the heavy chain or a fragment thereof of an antibody and two or more copies of a DNA encoding the light chain or a fragment thereof of the antibody; and a transformant.