MXenes represent a new family of 2D transition metal carbides and/or carbides that has attracted a great deal of attention in various applications because of their unique electrical, thermal, and mechanical properties. In this work, we report on the structure and crystallization behavior of poly(ethylene oxide)(PEO)/MXene nanocomposites. MXene Ti3C2Tx (where T is a surface termination) was synthesized and used as the nanofiller to form polymer nanocomposites using a solution blending method. Their mor-phologies, structures and crystallization behaviors were investigated using transmission electron microscopy, atomic force microscopy, polarized light microscopy, wide-angle X-ray diffraction and differential scanning calorimetry. Both non-isothermal and isothermal crystallization behaviors were studied. We show that the presence of 2D Ti3C2Tx accelerates PEO crystallization at very low MXene contents, while it inhibits PEO crystallization as the loading increases. The fastest crystallization rate was observed at 0.5 wt% MXene content. This was attributed to the competition of nucleation and confinement effect of the 2D filler. (C) 2016 Elsevier Ltd. All rights reserved.