Present work deals with the quantum mechanical study of the molecular structure of two wellknown voltage sensitive potassium channel blockers: 4, Aminopyridine and 3, 4 Diaminopyridine. The equilibrium geometry, harmonic vibrational frequencies and HOMO-LUMO gap have been calculated by the density functional theory (DFT), employing 6-311++G (2d, 2p) as the basis set. A detailed interpretation of the infrared and Raman spectra of 4, aminopyridine and 3, 4 Diaminopyridine in terms of the potential energy distribution (P.E.D) is reported. The similarities and differences between the vibrational spectra of the two molecules studied have been highlighted. The thermodynamic calculations related to the title compounds were also performed at B3LYP/6-311++G (2d, 2p) level of theory.