Polarized far-infrared spectra of aliphatic polyesters [–(CH2)z–CO–O–O]n with z = 1, 2, and 5 (z = 4, nonpolarized) and α-polyamide (nylon 6 and its N-deuteroderivative) have been measured in the region up to 80 cm−1. All these polymers have essentially planar zigzag conformations. The normal vibrations of these polymers were calculated for the far-infrared regions by using the Urey–Bradley force field with some modifications. For the series of polyesters, several far-infrared bands were found to appear systematically at nearly the same positions with similar intensities. The similarities between these series of bands of the polyesters and those of polyamides were interpreted from the point of view of the normal modes of vibrations.