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Exploring flexible dielectrics with high dielectric constant and low loss is pertinent for many applications in electronic devices. In the present work, a non-ferroelectric polymer, polyvinyl alcohol (PVA), was used to fabricate homogeneous dielectric composite films with a relatively high dielectric constant and a low dielectric loss by using 2D nano sheets (Ti3C2Tx MXene) as the filler. To limit dielectric loss, SiO2 was coated onto the surface of MXene to provide interfacial barrier effect and suppress dielectric loss. MXene@SiO2/PVA composite films showed lower dielectric losses at low frequencies (from 20 Hz to ~ 10 kHz) compared with MXene/PVA composite films. MXene@SiO2/PVA composite films with 2.5 wt% MXene loading and 5 wt% (with respect to MXene content) SiO2 coating had a dielectric constant of 27.2 (a 292.5% rise compared to neat PVA film) and a dielectric loss of only 0.057 (a 259.6% reduction compared to MXene/PVA composite film) at 100 Hz and room temperature (RT). In addition, this SiO2-coated composite film had stable dielectric properties (dielectric constant and loss change from 27.2 to 29.3 and 0.057 to 0.104, respectively) in the temperature range of RT to 60 °C. This work provides a promising way to fabricate PVA-based dielectric composites with excellent dielectric properties for practical applications in electronics.