Morocco has the most important deposits of phosphate in the world. The present paper aims to determine experimentally the isotherms of sorption of humid natural phosphate using the saturated salt method. The experiments are conducted at five temperatures which are: T = 30 degreesC, 40 degreesC, 50 degreesC, 60 degreesC and 70 degreesC, The experimental curves of sorption are then described by Henderson's, Guggenheim, Anderson, and Beer's and Brunauer, Emmet and Teller's models, The isotherms of sorption calculated by the three models are compared.