Highly saturated lithium- and cesium- graphite intercalation compounds (of a composition LiC2-LiC4, CsC4) synthesized under high pressure conditions were investigated using X-ray diffraction. It was shown an hexagonal unit cell with lithium with a = 8.63 Angstrom and c = 11.1 Angstrom (c = 3I(c)). With cesium, the orthorhombic unit cell presents the following parameters : a = 4.945 Angstrom, b = 8.565 Angstrom and c = 4 I-c = 23.48 Angstrom.