We investigated phase behaviors of polyimide blends such as polyethermide(PEI)/polystyrene(PS), PEI/polyamideimide(PAI), PEI/polyethyleneoxide(PEO), and PAI/PEO systems. Our sample systems exhibited lower critical solution temperature(LCST) phase behaviors. In the PEI/PS system, phase transition occurred near or above the glass transition temperature(Tg) of PS and the critical temperature of the system increased with decreasing molecular weight of PS. For PEI/PAI and PEI/PEO systems, the critical temperature of PEI/PAI system is higher than that of PEI/PEO system. Phase transition temperatures of PAI/PEO systems appeared near or below the melting point of PEO.