This study proposes a novel sepiolite-based Aquivion electrolyte membrane which could be operated at low relative humidity. In the study, it was discovered that the functionalization of sepiolite with fluorinated groups (i.e., -C7F15), named SEP-F, helps its dispersion in the composite membrane, compared with the use of natural sepiolite. The Aquivion/SEP-F composite membrane showed increased water uptake, thermo-mechanical and chemical stability as well as proton conductivity and decreased swelling compared with commercially available Nafion HP and pristine Aquivion. Their behavior in single cell MEA testing conditions was also assessed. Aquivion/SEP-F composite membrane can be an interesting alternative for low relative humidity operation of PEMFC (proton exchange membrane fuel cell).