Structural and optoelectronic properties of pure and Co doped In2 O3 are studied by employing the full-potential linearized augmented plane wave method,which is known to produce highly accurate results.First principles calculations are performed with ordinary generalized gradient approximation (GGA) along with new Hubbard and modified Becke-Johnson exchange (mBJ) potential techniques.Improved band gap results are obtained for In2O3 with GGA+U and mBJ.In the case of mBJ,the band gap values are 3.5eV and 3.4eV for rhombohedral and cubic phases,which are in close agreement with the experimental data.Substitution of In by Co 25％ alters the energy gap and a spin splitting effect is observed in these phases.For the spin-up state,it remains semiconductor,whereas for the spin-down state it shows semimetallic behavior.The value of static refractive index n(0) is 1.74 for the cubic phase,while in rhombohedral phase the values of n(0) are 1.77 and 1.74 along xx and zz optical axes,respectively.The calculated optical properties conform anisotropy in the rhombohedral phase and these materials can be potential candidates for the optoelectronics applications.