Herein, Ti3C2Tx (MXene) was synthesized and mixed with polyvinyl alcohol (PVA) to fabricate PVA/MXene nanocomposites. The results confirmed that delaminated MXene was successfully synthesized. The nanocomposites were obtained via casting/evaporation method. The thermal stability was evaluated by thermogravimetric analysis (TGA). For the PVA composites with content of 2 wt% MXene (PVA‐MXene2), the thermal decomposition was retarded by approximately 20°C when the temperature was lower than 350°C compared with that of pure PVA. Moreover, the evolved gas products of the PVA/MXene composite were lower than those of pure PVA. For the first time, the flame retardancy of PVA/MXene nanocomposite was investigated using a microscale combustion calorimeter. The peak heat release rate (PHRR) and total heat release of the PVA composite were reduced by 25.7% and 25.5%, respectively, with 1 wt% of MXene. The temperatures at PHRR of PVA/MXene composites were improved with the addition of MXene. Moreover, the addition of MXene resulted in PVA composites with a higher tensile strength and elongation at break than those of a pure PVA film. The improvements in the flame retardancy, thermal and mechanical properties of PVA/MXene composites should enable a wide range of potential applications of MXenes in polymer matrices.