Abstract In this paper, the stability, electronic and mechanical properties of three polymorphs of Fe2B were studied using CASTEP code. The calculated binding energy and formation energy values showed that Tp2 (Space group, I 4 ¯ 2 m ) and Tp3 (Space group, I 4 ¯ / mcm ) structures of Fe2B are more stable than Tp1 ( I 4 ¯ 2 m ) . Structural analysis results indicated that Tp2 and Tp3 have the same atom coordinate numbers. Electronic structure calculations revealed that both Tp2 and Tp3 have very similar chemical bonding states, the d orbital splitting reduced DOS density at Fermi surface result in total energy reduction when compared with that of Tp1, and is consistent with thermodynamical results. The covalent bonds in these structures are due to orbital overlap between p bands of B and d bands of Fe, but the whole system has a metallic character and DOS at Fermi level are dominated by d bands of Iron. Elastic constants were also evaluated and indicated that in order to improve the abrasive property of boron casting irons; Tp1 is better than the other two structures and has the largest bulk modulus and Young modulus values.