The behavior of phosphorous transfer from P₂O₅-containing CaO–SiO₂–Fe_tO slags to 2CaO·SiO₂ particles homogeneously dispersed in slag has been studied by using a microprobe analysis. The maximum phosphorus distribution ratio between 2CaO·SiO₂ particle and slag is obtained at the nose composition of 2CaO·SiO₂ primary phase region in CaO–SiO₂–Fe_tO phase diagram and the temperature dependence of this distribution ratio is small. The phosphorous transfer rate from slag to a 2CaO·SiO₂ particle with 20 to 50 µm is considerably fast and a 2CaO·SiO₂ particle changes to the particle with the composition of 2CaO·SiO₂–3CaO·P₂O₅ solid solution within 5 s. In the case of particles present in cluster, only the rim part (5 µm) of a particle changes to the composition of 2CaO·SiO₂–3CaO·P₂O₅ solid solution within 5 s, but small size particles with 3 to 8 µm completely change to the particles with the composition of 2CaO·SiO₂–3CaO·P₂O₅ solid solution within 5 s.