We have prepared new charge-transfer (CT) complex polymer blend membranes (CT membranes), for use as high performance polymer electrolyte membranes (PEMs); with a simple and easy preparation method for application in PEFCs. In this study, electron-accepting sulfonated polyimide (SPI) and electron-donating polyether (PE), were used to develop polymer-polymer type CT membranes. The formation of CT complex in the obtained SPI/PE membranes was confirmed by visible spectroscopy. The use of flexible spacers in the PE and heat treatment of the CT membranes, enhanced the CT complex formation. SPI/PE CT membranes showed 1.9-2.2 times higher mechanical strength than the original SPI, while SPI/PE 0.33 CT membrane with heat treatment at 130 degrees C for 2 h showed 4.3 times higher mechanical strength than the original SPI. Hydrogen permeability through SPI/PE CT membranes was 4.1-5.4 times lower than Nafion 212 and 1.4-1.9 times lower than the original SPI membrane. We have prepared a thin SPI/PE CT membrane (10 mu m thickness), that showed comparable OCV (0.88 V), similar resistance compared to Nafion 212 and demonstrated more than 10 h of durability in a fuel cell test; suggesting that SPI/PE thin CT membrane can be applied for PEFC application.