Abstract: The state of cosegregation of P and Ce at ferrite grain boundaries in iron has been studied using the conbination with XPS and computer modelling. The results indicate that the concentration of P is less, the P atoms at grain boundaries are solid solution state and the influnce of Ce on the chemical state of P at grain boundaries is very small.As the concentration of P at grain boundries is rather high,Ce may change the chemical state of P.The computer modelling shows that the chemical state of P at grain boundaries depends on its segregated structure.