The crystal structure of the complex, $[Mg(H_2O)_6](C_4H_4NO_4S)_2,$, was determined at 296 K. The unit cell parameters of the crystal structure are a=6.9404 Å, b=8.5775 Å, c=8.7200 Å, α=68.564°, β=78.640°, γ=81.260° and Z=1. The complex crystallizes in the centrosymmetric triclinic space group P-1. The Mg(II) ion is coordinated by six O atoms from six aqua ligands and in the crystal structure, the anions and cations are linked with three dimensions via O—H···O and O—H···N interactions. In addition to the structure which was obtained by X-ray diffraction technique, the theoretical structure was calculated by using density functional theory (B3LYP) with the 6-31G basis sets. The molecular electrostatic potential, frontier molecular orbitals and theoretical IR studies were calculated by using DFT method. Besides, the experimental IR spectrum and thermal analysis were investigated for the complex.