The study investigates the effects of boron additions (up to 0.4 wt% B) on the grain-boundary chemistry and tensile properties of Ni3Al containing 24-26 at.% Al. The ductility and fracture behavior of B-doped Ni3Al depend critically on deviations from alloy stoichiometry. As the aluminum content decreases below 25 at.%, ductility increases significantly, and the fracture mode changes from intergranular to transgranular. Auger studies indicate that boron segregation to grain boundaries increases, while the concentration of grain-boundary aluminum decreases with decreasing bulk aluminum concentration. These results suggest that alloy stoichiometry strongly influences grain-boundary chemistry, which in turn affects grain-boundary cohesion. Boron exhibits unusual segregation behavior in Ni3Al, tending to segregate to grain boundaries rather than free surfaces. In contrast, sulfur, an embrittlement impurity, tends to segregate more strongly to free surfaces. The beneficial effect of boron is consistent with existing theories of solute segregation effects on grain-boundary cohesion. The yield stress of B-doped Ni3Al decreases with increasing grain size produced by long-term annealing at 1000°C, following the Hall-Petch relation. The tensile elongation initially remains independent of grain size but shows a moderate decrease for grain diameters larger than 110 μm.The study investigates the effects of boron additions (up to 0.4 wt% B) on the grain-boundary chemistry and tensile properties of Ni3Al containing 24-26 at.% Al. The ductility and fracture behavior of B-doped Ni3Al depend critically on deviations from alloy stoichiometry. As the aluminum content decreases below 25 at.%, ductility increases significantly, and the fracture mode changes from intergranular to transgranular. Auger studies indicate that boron segregation to grain boundaries increases, while the concentration of grain-boundary aluminum decreases with decreasing bulk aluminum concentration. These results suggest that alloy stoichiometry strongly influences grain-boundary chemistry, which in turn affects grain-boundary cohesion. Boron exhibits unusual segregation behavior in Ni3Al, tending to segregate to grain boundaries rather than free surfaces. In contrast, sulfur, an embrittlement impurity, tends to segregate more strongly to free surfaces. The beneficial effect of boron is consistent with existing theories of solute segregation effects on grain-boundary cohesion. The yield stress of B-doped Ni3Al decreases with increasing grain size produced by long-term annealing at 1000°C, following the Hall-Petch relation. The tensile elongation initially remains independent of grain size but shows a moderate decrease for grain diameters larger than 110 μm.