PHOSPHORUS (P) AVAILABILITY IN ACID MINERAL SOILS IS OFTEN LIMITED DUE TO HIGH SORPTION CAPACITY, WHICH NEGATIVELY AFFECTS CROP PRODUCTIVITY. THE PURPOSE OF THIS RESEARCH WAS TO FIND THE MAXIMUM PHOSPHORUS SORPTION CAPACITY OF THREE TYPES OF ACID MINERAL SOILS, OXISOLS, ACID SULPHATE SOIL, AND ULTISOLS, USING THE LANGMUIR ISOTHERM MODEL. SOIL SAMPLES WERE COLLECTED AND ANALYZED IN THE LABORATORY WITHOUT TREATMENT TO ASSESS THEIR NATURAL P SORPTION CHARACTERISTICS. THE DATA OBTAINED WERE FITTED TO THE LANGMUIR EQUATION TO ESTIMATE THE MAXIMUM SORPTION CAPACITY (x_m) AND THE BINDING ENERGY CONSTANT (K_L). THE RESULT SHOWED THAT ACID SULPHATE SOIL HAD THE HIGHEST XM VALUE, FOLLOWED BY OXISOLS, WITH THE LOWEST IN ULTISOLS. THESE DIFFERENCES WERE CLOSELY RELATED TO VARIATIONS IN SOIL CHEMICAL PROPERTIES, ESPECIALLY FE AND AL OXIDE CONTENT AND SOIL PH, WHICH INFLUENCE THE NUMBER OF ACTIVE SORPTION SITES.