Giant magnetoresistance in the intermetallic compound<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">Mn</mml:mi></mml:mrow><mml:mrow><mml:mn>3</mml:mn></mml:mrow></mml:msub></mml:mrow><mml:mi mathvariant="normal">GaC</mml:mi></mml:math>

We have measured the transverse resistance of an intermetallic compound ${\mathrm{Mn}}_{3}\mathrm{GaC}$ in pulsed high magnetic fields up to 25 T. Giant magnetoresistance is observed due to the field-induced magnetic transition from the antiferromagnetic to the intermediate phase at low temperatures. The temperature dependence of magnetoresistance shows a dip at the Curie temperature. The dip can be explained using a simple model of de Gennes and Friedel based on magnetic critical scatterings. The normal Hall coefficient is found to show a striking change at the transition, suggesting that the giant magnetoresistance is caused by the change of the carrier concentration.