Results of inelastic neutron scattering (INS) study on normal and N-deuterated l-leucine are reported. The INS spectra of l-leucine show additional bands as compared with optical spectroscopic methods (IR and Raman scattering) in the energy transfer up to 800 cm - 1 . Both in normal and d 3 -l-leucine, extra bands correspond to out-of-plane γ(N-H ... O) at 522, 510 and 257 cm - 1 , and γ(N-D ... O) at 371 cm - 1 hydrogen bond vibrations respectively. Methyl and carboxyl groups vibrations are observed at 215, 232, 257 and 290 cm - 1 and 175, 535, 674 and 778 cm - 1 respectively.