We report on the observation of a strong reorganization of the proton hydration structure in hydrated Nafion membranes following single-quantum excitation of a proton vibration with ∼4 μm light pulses. The reorganization takes place with a time constant of 170 ± 20 fs and leads to a strong red shift of the excited proton vibration and the rise of new waterlike O-H stretch absorption bands. These observations can be explained from a vibrational-excitation-induced change of the proton-hydration structure that involves transfer of the proton charge. The results are consistent with recent quantum molecular dynamics simulations of proton transfer in Nafion membranes.