Development of a host cell capable of producing a glycoprotein composition such as an antibody composition which is useful in development of medicaments is desired. The present invention provides a cell in which a genomic gene encoding an enzyme relating to a sugar chain modification in which 1-position of fucose is bound to 6-position of N-acetylglucosamine in the reducing end through .alpha.-bond in a complex type N-glycoside-linked sugar chain is knocked out, wherein the cell is naturalized in a serum-free medium and a process for producing a glycoprotein composition using the cell.