The interaction between TNT and a biologically important molecule-melatonin-has been investigated at the level of density functional theory. The calculations showed that these molecules in vacuum conditions orient themselves almost parallel, face to face with each other. Various energies, physico-chemical, and quantum chemical properties of the system are computed. The calculated electrostatic charges, UV, and NMR spectra show the presence of a strong interaction between TNT and melatonin. However, presently, the nature of this interaction (whether an intimate pair or donor acceptor type p-complex formation) is not clear.