The magnetic susceptibility of lateritic soils and clays has been determined. A linear relationship between specific magnetic susceptibility and iron oxide content of kaolinitic and allophanic soils and clays has been observed. Montmorillonite and magnetite-bearing soils have shown high magnetic susceptibilities which were not related linearly to their iron oxide contents. Fe+++and Fe++ ion substitutions in the octahedral position of 2:1 types of clays were thought to be the probable cause of high magnetic susceptibility of such soils. The high values obtained for the latter may be attributed solely to the ferromagnetic property of magnetite. The type of bonding of Fe+++ion in octahedral coordination was investigated through spin-only moment (u. eff.) determinations. It was found that substitution of less than half a mole of Fe+++ion per unit cell in 2:1 types of clays appears to form electrostatic bonding (i.e., spin-free, sp3d2bonding), while more than half a mole of Fe+++ion per unit cell shows the covalent type of bonding (i.e., spin-paired, d2sp3bonding). The diamagnetic, paramagnetic, and ferromagnetic nature of kaolinite, montmorillonite, hematite, and magnetite, respectively, has been evidenced.