Acidic mineral soil generally has mild acidic to high acidic reaction or pH ⩽ 5.5, with very low exchangeable bases that can exchanged and rich in oxide as well as Al and Fe hydroxides. Acidized soil can lead to increased toxicity from aluminum, iron, and manganese element to the plants and deficiency of phosphorous, alkaline cation (calcium, potassium, and magnesium), and molybdenum element as well as soil microbial population. This study aimed to observe the fractionation distribution of metal aluminum (Al), iron (Fe), and manganese (Mn) and soil microbial population in acidic soil horizon. Al fraction parameters included exchangeable Al (Al-exc), non-crystalline Al (Al-o), inorganic non-crystalline Al (Al-po), Organically Bound Al (Al-p), Low- and Medium- Stability Complexes with Organic Matter (Al-Cu) and High-Stability Complexes with Organic Matter (Al-pCu), exchangeable fractionation of Fe and Mn (Fe/Mn-exc), Fe and Mn from Bound to Carbonates/Acid- extractable, Bound to Fe-Mn Oxides/Reducible, Bound to Organic Matter Fe Mn/Oxidizible, Fe- Mn Residual and soil microbial population (total microbes and Acidithiobacillus bacteria). The results, distribution of Al fraction on the upper horizon of Jasinga and Lebak were dominated by stabilized organic amorphous Al fraction with fluctuative decrease of organic matter (Al-pCu), while the lower horizon tended to be inorganic amorphous Al (Al-op). The fractionation distribution of Fe fractionation on Jasinga and Lebak was dominated by Oxidizible Fe fraction. Mn fraction distribution on Jasinga and Lebak were dominated by Mn-residual fraction in each acidic soil horizon. The total population of Microbes and Acidithiobacillus.sp in each soil horizon decreased along with the alteration of soil chemical properties in each soil depth horizon.

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