Composite membranes of sulfonated polyether ether ketone (SPEEK) are prepared with sulfonated fullerene as an additive by solution cast methodology for its use as polymer electrolyte in direct methanol fuel cells (DMFCs). Fullerene is functionalized by attaching sulfonic acid groups by formed precursor (4-benzene diazonium sulfonic acid) through diazotization reaction route. Functionalized fullerene is extensively characterized by FT-IR, XPS, H-1-NMR and elemental analysis to confirm the sulfonation. Structural changes in sulfonated fullerene (Sfu) are observed through FE-SEM and TEM analysis. The composite membranes prepared with varying Sfu content in SPEEK are characterized in terms of their physico-chemical properties in conjunction with ionic conductivity and methanol permeability. Oxidative stabilities of these composite membranes are compared with pristine SPEEK membrane. DMFC performance of these membranes is evaluated and the results are compared with pristine SPEEK and Nafion-117 membranes. Steady state polarization in DMFC for SPEEK-Sfu (0.5 wt. %) exhibits peak power density of 103 mW/cm(2) which is at par with Nafion-117 membrane. Membrane electrode assemblies comprising optimized SPEEK-Sfu (0.5 wt. %) and pristine SPEEK matrix are subjected for time evolution studies to evaluate steady state peak power densities. (C) 2015 Elsevier Ltd. All rights reserved.