Solid solutions of poly(ethylene oxide) of different molecular masses (M? from 6 x 105 to 4 x 106 g mol-1) and lithium perchlorate (LiClO4) were prepared by solution casting method. Salt concentrations of solutions vary between around 2 and 13 wt%. Thermodynamic properties of these solutions are reported in the range of low salt content. The solutions represent two-phase systems mostly not in equilibrium at room temperature. They consist of neat crystalline PEO and an amorphous mixture of salt and polymer. Crystallinity of PEO in salt solutions stays constant with increasing salt content and is independent of molecular mass. Crystallinities serve determining share and composition of the amorphous phase. Glass transition temperature increases linearly with salt content in the amorphous phase. Depression of equilibrium melting points by addition of salt provides activity coefficients in solutions and allows for estimation of degrees of dissociation. Rate of crystallization of poly(ethylene oxide) depends exponentially on inverse undercooling. In that way, it is also coined by equilibrium melting point depression. POLYM. ENG. SCI., 2012. (C) 2012 Society of Plastics Engineers