Large negative magnetoresistance in the antiferromagnet <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mi>BaMn</mml:mi><mml:mn>2</mml:mn></mml:msub><mml:msub><mml:mi>Bi</mml:mi><mml:mn>2</mml:mn></mml:msub></mml:mrow></mml:math>

A very large negative magnetoresistance (LNMR) is observed in the insulating regime of antiferromagnet ${\mathrm{BaMn}}_{2}{\mathrm{Bi}}_{2}$ when a magnetic field applied perpendicular to direction sublattice magnetization. high eventually suppresses behavior and allows reenter metallic state. This effect seemingly unrelated any field-induced phase transition, as measurements susceptibility specific heat did not find anomaly function fields at temperatures above $2\phantom{\rule{0.28em}{0ex}}\mathrm{K}$. The LNMR appears both current-in-plane current-out-of-plane settings, Hall effects suggest that its origin lies an extreme sensitivity conduction processes holelike carriers infinitesimal canting LNMR-induced state may thus be associated with breaking antiferromagnetic parity-time symmetry by and/or intricate multiorbital electronic structure ${\mathrm{BaMn}}_{2}{\mathrm{Bi}}_{2}$.