A series of poly(phthalazinone ether ketone) bearing flexible pendant quaternary ammonium groups (QA-PPEKx) are prepared. The structure of the as-prepared polymers is confirmed by H-1 NMR spectroscopy. The resulting ionomer membranes present good film-forming properties. The QA-PPEK-x membranes showed IECs in range of 1.22-1.62 mmolg(-1), and hydroxide conductivity of 0.044-0.092 &cm(-1) at 80 degrees C. The water uptake of the QAPPEK-x membranes are 20.1-78.2% at 30 degrees C and 30.2-89.7% at 60 degrees C while the swelling ratio are 6.0-21.8% at 30 degrees C and 9.6-37.1% at 60 degrees C, respectively. The morphology of the membranes characterized by atomic force microscope (AFM), showed well-defined microphase separation structure. The resulting QA-PPEK-x membranes demonstrated excellent thermal stability, mechanical properties and alkaline stability.