Phosphate (P) sorption and desorption characteristics have been investigated for sixty-two representativesamples of the major Thai upland agricultural soils which are Oxisols and Ultisols formed on diverse parentmaterials and under various climatic conditions. P sorption characteristics are well described by Langmuir andFreundlich equations. Values of Langmuir P sorption maximum (Xm) and b coefficient range from 47 to1250 μg g−1 soil and 0.5 to 30 mL μg−1, respectively and the Freundlich k varies between 12 and 1694 μg g−1and B coefficient 0.09 and 0.67. Soils derived from basalt have larger values of P sorption maximum than soilson other parent materials. Both P sorption maximum and Freundlich k are closely related to pH (NaF), SSA,total titanium, aluminum and iron, dithionite and oxalate extractable Fe and Al, and other soil properties thatreflect specific surface area. Soil pH in NaF is highly effective in predicting the P sorption capacity of Thai uplandsoils explaining 79% of the variation in P sorption by these soils. P desorption curves for adsorbed P are welldescribed by the Freundlich equation. The Freundlich kd coefficient for P desorption is highly, linearly related tothe Freundlich k coefficient of P sorption indicating that the above soil factors that contribute to P sorption similarly affect P desorption. © 2009 Elsevier B.V. All rights reserved.