Acid sulf ate soils in Peninsular Malaysia are characterized by low pH and high amounts ofAl Alleviation of toxic ions in the soils by controlled drainage is recommended. However, potential acidity remains in the soils due to slow release of toxic ions during mineral weathering. A study was conducted to determine the release of AI and other ions by repetitive extraction of samples from the field and by aerobic incubation of samples in the laboratory. The results showed that Al was released continuously from the soils even after the sixth extraction. When the soils were allowed to undergo free oxidation under aerobic conditions Al, Mn, Fe, Ca, Mg, K, Na and S were released into the soil solutions due to breakdown of clay minerals. Activities of these ions increased significantly, resulting in an increase of electrical conductivity of the soil solution. Additionally, pH of the soil solution dropped. These commonly observed properties of acid sulfate soils have great implications on their management practices.