Keywords: FeSi 2 , first-principle, band structure, density of state. Abstract. Electronic structures and optical properties of bulk β-FeSi 2 are investigated in detail by first principles pseudo-potential methods based on the density function theory. The calculated results show that β-FeSi 2 is a quasidirect band gap material with gap value of 0.74eV. The density of states is mainly composed of Fe 3d and Si 3p states. The dielectric constant, absorption coefficient, and the conductivity are also given. The results are compared with previous theoretical calculation and the available experimental data.