Profile fitting procedures associated with integral breadth studies and Fourier analysis are applied to the study of the complex Bi-containing layered perovskite SrBi 2 Nb 2 O 9 . Strong line broadening anisotropy is evidenced. Both `size' and `strain' effects contribute to the observed width. However, `size' broadening along the [00 l ] direction is essentially caused by stacking faults. The coherently diffracting domain sizes are deduced from Fourier analysis of the diffraction patterns and a rough estimate of the mean distance between faults is given. Thermal annealing significantly decreases the stacking fault density.