Disclosed is a method for producing a recombinant antibody efficiently and at a low cost. Specifically disclosed is a method for producing an antibody or a fragment thereof, which comprises producing the antibody or the fragment thereof by using a cell which contains a higher copy number of foreign DNA encoding an L-chain of the antibody or a fragment thereof compared with the copy number of foreign DNA encoding an H-chain of the antibody or a fragment thereof. Also disclosed are: a recombinant vector carrying one copy of DNA encoding an H-chain of an antibody or a fragment thereof and two or more copies of DNA encoding an L-chain of the antibody or a fragment thereof a transformed cell and others.
