Abstarct: Gallium nitride (GaN) is one of the semiconductor compounds of the III-V group. There are two types of its structure; wurtzite and zinc blende. The band gap of this compound is direct type. In the wurtzite phase, it has a band gape of about 3.5 eVand in the zinc blende phase, has a band gape of about 3.2 eV. In this study, the electron structure and optical properties of pure gallium nitride, and doped with Al and In atoms investigated in both wurtzite and zinc blende structure. The calculations of pure and doped structure in both wurtzite and zinc blende phases were performed using the density functional theory (DFT) and Local Density Approximation (LDA) approach by the SIESTA computational code. In the study of the electron structure of the compound, the electronic band structure and the total and partial density of states were calculated. The study of optical properties also includes the investigation of dielectric function, refractive and extinction coefficients, reflectivity, optical absorption coefficient and conductivity. The calculations of the density of the states and band structure showed that the Alx Ga1-x N alloy is a direct band gap semiconductor. The band gap increases with increasing impurity concentration. This increase in the band gap also shows itself in the dielectric function diagram as the displacement of the absorption edge towards the higher energies. Finally, the electron structure and optical properties of gallium nitride alloy with indium were investigated at concentrations of 0.0625, 0.125, 0.25 and pure InN. The calculations relating to the density of states and band structures showed that gallium nitride doped with indium impurity is a semiconductor with a direct band gap. The band gap is reduced by increasing the indium impurity concentration and the mextallic property intensifies in the material, and thus the conductivity increases.