Abstract: The influences of Ce and P on embrittlement transition temperature in Mn steel has been investigated by impact test, SEM, TEM and Auger spectrometer. The results indicate that the segregation of phosphorus along the austenitic grain boundary increases the embrittlement transition temperture, and Cerium adding to steel can minimize the degree of segregation and improve the impact toughness, therefore the embrittlement transition temperature is decreased.