ABSTRACT:The amount of total phosphorus (P) and its chemical forms were investigated in sediments of the Eastern Coast of Thailand in the dry (April 2001) and wet (July 2001) seasons. The amounts of total P ranged from 55.83 to 2,575.83 and from 30.0 to 2,672.50 µg g -1 dry weight for the dry and wet seasons, respectively. The P in sediments was mainly in an inorganic rather than organic form. Sediment inorganic P fractions were determined by a sequential extraction technique. In the estuarine sediments, the major form of P was Fe, Albound P and the second most abundant form was organic P, whereas the other sediments showed different relative dominant P forms depending on the sediment characteristics of each location. The seasonal change had an influence on the chemical form of P available. In the dry season the available fractions were derived from organic P, those in the wet season were derived largely from Fe, Al-bound P. The available concentrations found for both seasons were very similar in terms of the percentage of total P. It was also found that in most samples, the available forms were very low, comprising less than 10 % of total P.In this study Fe oxides were found to be the major P sorbent of the sediments, followed by clay contents, while organic matter and CaCO 3 were less effective in sorbing P. In addition, the sediment P concentrations decreased with increasing sediment pH and salinity of the overlying water.