[en] This work presents results of terahertz time-domain spectroscopy (THz-TDS) investigations of two types of polymer-based nanocomposites, consisting of bulk samples of graphene nanoflakes embedded in a polymer matrix and thin films where single-walled carbon nanotubes (SWCNTs) with a chiral index (7,5) were wrapped in single strains of a polymer. Our THz-TDS setup is a room-temperature system with a frequency range of 0.1 to 3.5 THz, based on photoconductive switches as both the emitter and detector, excited by 100-fs-wide optical pulses. We have studied THz spectra of both types of samples and compared them to the ones obtained for the pure polymer reference specimens and fitted the experimental complex conductivity data to the Drude–Smith model. The Drude–Smith model fits our data well, demonstrating that graphene nanoflakes and SWCNTs, exhibit highly localized intra grain/tube electron backscattering with a femtosecond relaxation time. (paper)