Since Bacillus anthracis is a high-risk pathogen and a potential tool for bioterrorism, numerous therapeutic methods including passive immunization have been actively developed. Using a human monoclonal antibody phage display library, we screened new therapeutic antibodies for anthrax infection against protective antigen (PA) of B. anthracis. Among 5 selected clones of antibodies based on enzyme linked immunosorbent assay (ELISA) results, 7B1 showed neutralizing activity to anthrax lethal toxin (LT) by inhibiting binding of the domain 4 of PA (PD4) to its cellular receptors. Through light chain shuffling process, we improved the productivity of 7B1 up to 25 folds. The light chain shuffled 7B1 antibody showed protective activity against LT both in vitro and in vivo. Furthermore, the antibody also conferred protection of mice from 3 x LD50 challenges of fully virulent anthrax spores. Our result expands the possibility of developing a new therapeutic antibody for anthrax cure. (C) 2018 Elsevier Inc. All rights reserved.