In this work, we investigated electronic and optical properties of TIN (thallium nitride) nanosheet using density function theory (DFT) implemented in Wien2k code. We calculated the dielectric function, absorption coefficient, optical conductivity, refraction index, extinction index, reflectivity, and energy loss function of the TIN nanosheet within GGA (PBE) approximation in both directions E parallel to x (electric field parallel to nanosheeet) and E parallel to z (electric field perpendicular to nanosheet). we also calculated the band gap energy within GGA (PBE) and GGA (PBE) + SO approximations. Optical conductivity in directions to x and z shows that TIN nanosheet has semiconductor properties especially in direction z. At the end, we calculated electronic and optical properties, and elastic constant of TIN bulk (wurtzite). (C) 2016 Elsevier GmbH. All rights reserved.