The structural, elastic, electronic, and optical properties of orthorhombic ZrPtSi and TiPtSi ternary compounds are investigated using the norm-conserving pseudopotentials within the generalized gradient approximation (GGA) in the frame of density functional theory. The calculated lattice parameters have been in agreement with the available experimental data. The second-order elastic constants have been calculated, and the other related quantities such as the Young's modulus, shear modulus, Poisson's ratio, anisotropy factor, sound velocities, and Debye temperature have also been estimated. The electronic structure of ZrPtSi and TiPtSi compounds are calculated by using the first principles GW and GGA approximations. The real and imaginary parts of the dielectric function and the optical constants such as the optical dielectric constant and the effective number of electrons per unit cell are also presented. (C) 2012 Elsevier B. V. All rights reserved.