A ferrallitic soil sequence from red to yellow developed on carbonate rocks in Cuba is studied. Clay content is very high (80 to 90 %) and composition differs mainly in the relative proportion of hematite and goethite. The main modification concerns the organization of constituents. Kaolinite crystallites are very small and independent in yellow soil resulting in a massive fabric. These crystallites are associated in red soil giving one μm aggregates and micropeds (500 μm). Higher Al content (TEM + microprobe) suggests that the cement is more an Al than an Fe coating. Soil compaction and consequent waterlogging are likely to be responsible for such a soil structure evolution. CEC, specific surface and porosity are different in the two kinds of soils and then all the physical properties.