Herein, we report terahertz (THz) shielding of flexible MXene (Ti 3 C 2 T x )/MWCNT/PVA polymer composite films by using THz time-domain spectroscopy (THz-TDS) in 0.1–2.0 THz frequency range. The polymer composite with 42 µm thickness exhibited an excellent shielding effectiveness of 36 dB at 2 THz which is much higher than most of the reported materials for THz shielding with comparable thickness. The absorption coefficient increases from 100 cm −1 for pristine PVA to ~ 600 cm −1 for 20 wt% MXene/1.5 wt% MWCNT/PVA composite. The high THz shielding of flexible MXene/MWCNT/polymer composite is ascribed to the good electrical conductivity and interfacial synergistic effect of 1D/2D nanostructures that promoted the shielding of electromagnetic waves. Our simple solution casting methodology for fabrication of thin films and subsequent high THz shielding opens possibilities to design MXene-based polymer composites for THz applications.