Abstract: The grain boundary is an interface, and the surface tension is one of its important thermodynamic property. In this paper, the surface tension of the grain boundary for α-Fe,Σ= 9 at various temperatures and pressures is calculated by means of Computer Molecular Dynamics (CMD). The results agree satisfactorily with the experimental data. It is shown that the contribution of entropy to surface tension of- grain boundary can be ignored.The grain boundary is an interface, and the surface tension is one of its i...