Abstract Grain boundary diffusion of Cr in  symmetrical Nb bicrystals with varying tilt angles, θ, was investigated in the temperature range of 958–1197°C. For low angle boundaries, the grain boundary diffusion is dominated by the dislocation pipe mechanism, in which the activation energy Q′ is independent of θ and the pre-exponential factor (sD′δ)0 varies linearly with sin(θ/2). For high angle boundaries, the grain boundary diffusion coefficients, sD′δ, fall into minima, whereas the activation energies Q′ attain maxima at the CSL boundaries, ∑13 (22.6, 67.4°), ∑17 (28.1, 61.9°) and ∑5 (36.9, 53.1°). The pre-exponential factor (sD′δ)0 also varies with θ, but the variation is random. The results of the study agree with those of the f.c.c. system, confirming that grain boundary diffusion is strongly affected by the boundary structure and associated energies.