The combination of polymer and ionic liquid (IL) is attracting increasing attention because of its versatile and tunable properties. In this paper, the IL 1-(2-hydroxyethyl)-3-methylimidazolium chloride ([HOEtMIM] CO, which has a complementary structure with poly(vinyl alcohol) (PVA), was adopted to act as a novel plasticizer for PVA to improve its thermal processability. The results demonstrated that the hydroxyl group and Cl- in the IL formed strong hydrogen bonds with the hydroxyl groups of PVA, thus efficiently confining its crystallization, decreasing its melting point, and obtaining a wide thermal processing window, up to 110 degrees C. The resultant PVA/IL composites showed high ionic conductivity, up to 2.82 X 10(-3) S/cm, and considerable flexible mechanical properties with an elongation at break of 317% when the IL content was 35 wt %, opening the potential applications of PVA in the field of flexible semisolid state electric double-layer supercapacitors (EDLC) and proton exchange membranes (PEM).