In the present study, porous structure of raw and calcined phosphate ore particles was examined. The specific surface area and the pore volume were determined by nitrogen adsorption. Raw particles and calcined ores were leached using dilute phosphoric acid solution (4% P₂O₅). In all cases, the ESEM (Environmental Scanning Electron Microscopy) observations show that the grain of phosphate holds its shape ovoidale. The sample heated at 780?C presented the lowest specific surface area 0.6 m²/g at each reaction time, and the unreacted phases were analysed using XRD, FT-IR, Nitrogen adsorption and ESEM observations. The selective leaching curves were evaluated in order to test the validity of kinetics models. A mathematical model in the following form was applied. The dissolution of the two samples (raw and calcined phosphate) has been observed to take place in two steps: the first being fast and the second being slow.