The surface atomic structure of MgCl2 crystalline particles and MgCl2-supported Ziegler catalysts was observed by means of high resolution transmission electron microscopy. Step-terrace surface structures, characteristic of the structure of the MgCl2 crystal, are found in the observed images of MgCl2 particles. The observation of the structure of MgCl2-supported Ziegler catalysts shows that the MgCl2 crystals are severely deformed by the processes of catalyst preparation. Due to the preparation procedure used the structure of the catalyst changes from crystalline to amorphous.