A systematic study of the dependence of the Grain Boundary Diffusion Process (GBDP) on texture using Dy and Dy-Nd-Cu in microcrystalline sintered and nanocrystalline hot deformed Nd-Fe-B magnets was performed. Diffusion parallel or perpendicular to the texture direction, the nominal c-axes orientation in the polycrystals, was investigated. By measuring thin slices from the respective samples, coercivity as a function of (i) magnet thickness and (ii) diffusion depth was obtained showing that GBDP efficiency depends on the diffusion direction, diffusion source as well as the grain morphology originating from the magnet production route. In nanocrystalline hot deformed magnets perpendicular diffusion is superior due to the platelet-like shape of the grains. Microcrystalline sintered magnets consist of equiaxed grains hence the main effects originate in anisotropic lattice diffusion and pole surface hardening. The magnetic properties are correlated with a comprehensive analysis of microstructure, chemistry and magnetization reversal. •Comparing texture's effect on GBDP in Dy, Dy-Nd-Cu in microcrystalline sintered & nanocrystalline hot deformed magnets.•GBDP efficiency relies on diffusion direction, source, and grain morphology from the magnet production route.•Perpendicular diffusion is more effective in hot deformed (nanocrystalline) magnets due to their platelet-like grain shapes.•Comprehensive analysis links magnetic properties with microstructure, chemistry, and magnetization reversal studies.