Normal mode analysis and their dispersion for poly(L-isoleucine) are reported by using Urey Bradley force field and Fourier transform IR. The calculated frequencies are found to be in reasonably good agreement with the Fourier transform IRspectra. Experimental measurements reported by Wunderlich et al. also support the calculated specific heat variation of poly(L-isoleucine).2010 Elsevier B.V. All rights reserved.