A theoretical and experimental study of Grain boundary structure in B doped Ni₃Al was carried out. Geometrical modelling was done to obtain the grain boundary structure in Ll₂ compounds for different misorientations between two grains. The size of interstitial sites in these boundaries was calculated to understand the segregation of B to the boundaries. Ratios of the B-B equilibrium interatomic distance to the nearest neighbour distances in various (A₃B) Ll₂ compounds were calculated, in an attempt to predict the grain boundary fracture behaviour in these compounds. Selected area channeling patterns were obtained from a number of grains to solve for the orientation relationship between grains, in order to predict the structure of the boundaries between them. A distribution of grain boundary structure that is different from the distribution for an undoped Ni₃Al is obtained in this work and is compared with results from other investigators. / M.S.