Abstract The structural characteristics of BaNb 5.67S 10.8 were studied using high resolution transmission electron microscopy (HRTEM). The BaNb 5.67S 10.8 crystals are composed of overlapped parallel flakes lying in the (001) plane of the hexagonal system. The misorientations displayed in the selected area electron diffraction (SAED) patterns indicated the presence of rotational stacking faults around the c-axis. The HRTEM image showed that cleavage appeared preferentially between a Ba–S layer and the successive S layer. The occurrence of the structural imperfections was found to relate to the weak bonding between Ba and Nb on the one hand, and Nb and S on the other hand in the octahedron. The formation of a 3 a×3 a two-dimensional superlattice was observed by electron diffraction. This was suggested to be due to atom ordering in the Ba–S hexagonal net.