Anthrax Immune Globulin (AIG) is a polyclonal anthrax immunoglobulin product developed by Cangene (Winnipeg, Canada) and Emergent BioSolutions (Rockville, MD). It is derived from plasma of individuals who have been vaccinated with BioThraxTM. It is a candidate for intravenous post-exposure treatment in patients with symptoms of anthrax disease. This study used the equine antitoxin as an alternative for anthrax medical counter measure. Methods: Horses were immunized intramuscularly with AVA (Anthrax vaccine adsorbed; BioThraxTM). The sera were examined with anti-PA (Protective Antigen) ELISA and TNA (Anthrax toxin neutralization assay). The passive protection test was performed with ATCC 14186 strain spores and equine sera in A/J mice model. Results: The sera from horses immunized with AVA have high titer in anti-PA ELISA, and stable neutralization activity in TNA in vitro. In a well-controlled A/ J mice animal model, the serum repeatedly and accurately protects A/J mice from exposure to a lethal challenge of the ATCC 14186 strain of Bacillus anthracis. Conclusions: Anthrax equine antitoxin shows a high titer and high neutralization activity, both in vitro and in vivo.