ABSTRACT The present work presents a detailed and through investigation of the electronic structure and spectra of 5,6-diphenyl -1,2,4-triazine derivatives . The ultimate aim , however , is to pinpoint those structural factors that underlie the biological activity and industrial application of these class of compounds . The ground state geometry of the studied compounds were determined using Density Functional Theory (DFT) at the level of B3LYP/6-31G**.The effect of substituent's of different electron-donating (accepting) strengths on the geometry and the electronic structural factures of 5,6-diphenyl -1,2,4-triazine was examined . The results of MO's Calculations are interpreted via ionization potential , electron affinity , energy gap , dipole moment , net charge ,charge density maps at HOMO and LUMO.The electronic absorption spectra in the UV region were measured using polar (ethanol) and non-polar (dioxane) solvents . Comparison between the experimentally observed and theoretically computed (MINDO/3 and ZINDO/S) Spectra in addition to a quantitative assignment of all transitions observed , were given. The computed state dipole moment is used to indicate the polarity of the excited state and hence predicts it's solvent dependence.