AM1, PM3 and DFT methods were used to study on the hydrogen-bonded dimer of melamine and [1,3] dioxane-2,4,6-trione. The electronic spectra, IR and NMR spectra of some complexes were calculated with INDO/SCI, AM1 and B3LYP/6-31G(d) methods, respectively. It is demonstrated that the negative stability energy is responsible for the formation of the complexes. Stabilization energies of these complexes were altered among the variations of electric property and steric effects of the monomers. HOMO-LUMO energy gaps were shrunk and the blue-shift of absorptions in the electronic spectra occurred. The vibrations of N-H bonds and chemical shifts of the protons changed with the formation of hydrogen bonds.