Layered zirconium phosphate (ZP) that bears fluorinated alkyl chains bonded covalently to the layers (ZPR) was used as a nanofiller in membranes based on a short-side-chain perfluorosulfonic acid (PFSA) to mechanically reinforce the PFSA hydrophobic component. Compared to the pristine PFSA, membranes with a ZPR loading up to 30 wt % show enhanced mechanical properties, and the largest improvement of elastic modulus (E) and yield stress (σY) are observed for the 10 wt % ZPR membrane: ΔE/E up to 90 % and ΔσY/σY up 70 % at 70 °C and 80 % relative humidity (RH). In the RH range 50–95 %, the in-plane conductivity of the composite membranes reaches 0.43 S cm−1 for 10 wt % ZPR at 110 °C and is on average 30 % higher than the conductivity of the pristine PFSA. The 10 wt % ZPR membrane is as hydrated as the neat PFSA membrane at 50 % RH but becomes progressively less hydrated with increasing RH both at 80 and 110 °C. The fuel cell performance of this membrane, at 80 °C and 30 % RH, is better than that of the unmodified PFSA.