We describe the LCST-type phase behavior of poly(ethylene oxide) (PEO) (M = 5000 and 20000) dissolved in 1,3-dialkylimidazolium tetrafluoroborate ionic liquids. The phase transition temperatures were identified using cloud point measurements. In these PEO/ionic liquid systems, liquid-liquid phase separation is observed in the temperature range from 130 to 170 °C. We report unusual temperature-composition phase diagrams in which the cloud point curves are strongly asymmetric, with the critical composition (wc) shifted to high concentrations of PEO. The critical temperature (Tc) and the critical composition (wc) of these systems are not a strong function of the molecular weight of PEO. In addition, the values of the LCST increase as the length of the alkyl chain in the imidazolium cation increases. By using ionic liquid blends as solvents, the LCSTs can be tuned by varying the mixing ratio of two ionic liquids.