The structural, mechanical, electronic and optical properties of ScN nitride in NaCl-B1, CsCl-B2, zinc-blende (ZB)-B3 and NiAs-B8 phases were investigated by first-principle density functional theory. Mechanical properties are investigated, and the ScN in NaCl-B1, ZB-B3 and NiAs-B8 phases are mechanical stable indicating possible experimental synthesis except for CsCl. We note that NaCl-B1 possesses the highest hardness of 24.8 GPa. Band structures and densityof states analysis indicate that NaCl-B1, ZB-B3 and NiAs-B8 are semi-conductors with energy bandgaps of 0.623, 2.517 and 0.471 eV, while CsCl is metallic with no bandgap. The electron charge density analysis for all ScN phases shows acharge transfer between Sc and N attributing to their electronegativity. The optical properties of ScN phases are investigated. The maximum reflectivity of ScN in CsCl-B2, NaCl-B1, NiAs-B8 and ZB-B3 phases are 0.5 to 0.56 with a photonenergy range of 7.5–10 eV. The ScN phases indicate the strongest absorption in the energy range of 0–4 eV. The refractive index for ScN in the energy range of 7.5 to 10 eV phases indicates that the extinction coefficient k is greater than the phase velocity n, showing no light propagation. On the other hand, the phase velocity n is greater than the extinction coefficient k at 0 to 4 eV and 11 to 15 eV energy ranges for all the ScN phases with excellent light propagation, consistent with the conduction curves.