This talk will discuss the photoexcited carrier dynamics of low dimensional nanomaterials studied by using time resolved optical pump-terahertz probe spectroscopy. The studies include the carrier dynamics of single layer and bilayer graphene, single walled and double walled carbon nanotubes, transition metal di-chalcogenides and organometal halide perovskites. In single layer graphene, the real part of photoconductivity ()), was found to be negative at high doping and positive at low doping throughout the spectral range of 0.5-2.5 THz. In contrast, for moderately doped bilayer graphene, real part of ) was negative at low frequency and positive on high frequency part of the spectra. In addition, hydrogen doping changed the sign of ) from negative to positive. Boltzmann transport theory including the energy and temperature dependence of scattering rate can describe such transition of ) quantitatively. These transitions arise from shift of Fermi energy, rise of carrier temperature, variation of band structures and the dominant scattering mechanism. The role of several kind of scattering rates will be discussed as graphene exhibits short-range scattering arising from ripples, grain boundaries etc, long-range Coulomb scattering, acoustic phonons, and surface-optical phonons scattering. Next, THz conductivity of single walled and double walled carbon nanotubes will be discussed for before and after photoexcitation conditions. Prior photoexcitation, prominent plasmonic peaks were observed for both the nanotubes. But after photoexcitation, the spectral signature of ) were opposite which will also be presented in this talk. At the end, the carrier relaxation of transition metal di-chalcogenides and perovskites will be discussed. These materials showed faster carrier relaxation at higher pump fluence which was understood by rate equation model incorporating three-body Auger scattering, bimolecular recombination, defect-mediated Auger scattering of electrons, holes, and excitons.