The structures of 1,4-diiodo-2,5-dimethylbenzene (1) and 1,3,4,6-tetraiodo-2,5-dimethylbenzene (2) are determined by single crystal X-ray diffraction. The packing motif in 2 is mainly determined by π-stacking and the system of halogen⋯halogen contacts between the stacks. In the structure of 1, it is determined by the presence of both π-stacking and the interaction between σ-holes of iodine atoms and the π-system of the neighboring molecules. The thermal stability of 1 and 2 is studied and the optical spectra are measured.