Tantalum( V ) chloride (TaCl 5 ) was intercalated into highly oriented pyrolytic graphite and into natural graphite flakes. X-ray diffraction measurements show that second stages were obtained. The fresh intercalation compounds were investigated by scanning tunneling microscopy in air and by electron diffraction. The commensurate (Η°7ΓΗ°7) superlattice of tantalum( V ) chloride shows a rotation of Β±19.1Β°against the graphite lattice. Additional superstuctures of longer dimensions were detected by scanning tunneling microscopy. A Moire Β΄pattern and some bands were observed. The graphite intercalation compounds were immersed in water for two hours at room temperature and dried at 100Β°C in air. X-ray diffraction showed that the original stages were preserved after exposure to water. The scanning tunneling micrographs of samples exposed to water show a pattern similar to that of pristine graphite, the superlattice had disappeared. Electron diffraction studies on such samples gave evidence that the intercalate is rearranged and forms amorphous layers. In the case of water-immersed samples, no surface structures of the intercalate were observable with scanning tunneling microscopy.