Lithium solid polymer electrolytes (SPE) composed of polyethylene oxide (PEO) and yttrium oxide (Y(2)O(3)) nanoparticles were prepared. The influence of the Y(2)O(3) nanoparticles on the non-isothermal crystallization behaviors, crystal structure, and conductive properties of the SPE were investigated. The peak temperature, crystallinity, and crystallization half-time (t(1/2)) of the SPE were strongly dependent on the concentration of Y(2)O(3) and the cooling rate. The non-isothermal crystallization data were analyzed by the modified Avrami model, which successfully described the nonisothermal crystallization process of the SPE. The Avrami exponents suggested that the Y(2)O(3) nanoparticles significantly affected both the nucleation mechanism and crystal growth of the PEO matrix. The nucleating and crystallization activation energies (psi and E(c)) estimated with different theories indicated that the Y(2)O(3) nanoparticles were inclined to serve as heterogeneous nucleating agents to benefit the crystallization at lower concentration whereas as physical hindrance to inhibit the crystal growth at relatively higher concentration. The maximum conductivity (sigma) of 5.95 x 10(-5) S cm(-1) at room temperature for the SPE was obtained at the Y(2)O(3) weight ratio of 0.10. POLYM. ENG. SCI., 51:2526-2534, 2011. (C) 2011 Society of Plastics Engineers