The uniaxial tensile properties of a B2 Fe-40Al based alloy containing 0.7 at.% carbon and 0.5 at.% boron have been obtained at room and elevated temperatures in air as a function of strain rate and compared to the response of a similar alloy without boron (i.e Fe-40Al-0.6C). Furthermore, tests were also conducted as a function of strain rate in oxygen at room temperature to elucidate the effect of environment on these properties. Both alloys contain a dispersion of a perovskite carbide within the grains and at grain boundaries. In addition, the quaternary alloy contains a fine dispersion of metastable borides and complex faults within the grains. Yield stress and tensile elongation appear strain rate insensitive (in the regime tested) for the boron-containing alloy at room temperature in oxygen, whereas some loss in elongation is encountered at the slowest rate in the ternary alloy; in all cases, fracture path is intergranular. In air, at room temperature, a strong strain-rate dependence of elongation is recognized in both alloys, their response being identical at the faster rates but diverging at the slow rates. A strong correlation is noted between the increase in percent transgranular cleavage and the drop in tensile elongation. The brittle-to-ductile transition temperature is sensitive to strain rate, shifting to higher temperatures rapidly with increasing strain rate. A variety of fracture paths is encountered depending on test temperature and strain rate.