Abstract The effects of boron additions (up to 0.4 wt% B) on grain-boundary chemistry and tensile properties of Ni3Al containing 24–26 at.% Al were studied. Room-temperature ductility and fracture behavior of B-doped Ni3Al depended critically on deviation from alloy stoichiometry. As the aluminum content of B-doped Ni3Al is decreased below 25 at.%, the ductility increases dramatically and the fracture mode changes from intergranular to transgranular. Auger studies indicate that the intensity of boron segregation to grain boundaries increases and the concentration of grain-boundary aluminium decreases significantly with decreasing bulk aluminum concentration. These results suggest that alloy stoichiometry strongly influences grain-boundary chemistry which in turn, affects the grain-boundary cohesion. Boron exhibits an unusual segregation behavior in Ni3Al, i.e. it has a strong tendency to segregate to the grain boundaries but not to cavity (free) surfaces. On the other hand, sulfur, an embrittling impurity, tends to segregate more strongly to free surfaces than to grain boundaries. The beneficial effect of boron is in agreement 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 The yield stress obeys the Hall-Petch relation: σ y = α o,y + k y d 1 2 with σy = 163 MPa and ky = 8.2 MPa cm 1 2 . The tensile elongation was initially independent of grain size, and showed only a moderate decrease from about 50–40% with grain diameters larger than 110μm.