Picosecond time-resolved total internal reflection fluorescence spectroscopy was applied to analyze the proton transfer reaction of 1-naphthol in water—sapphire interface layers. The rate constant of the proton transfer reaction from excited neutral species became slow in the interface layer as compared with that in the bulk aqueous solution. The anomaly observed up to the penetration depth of 100 nm was interpreted in terms of rotational fluctuations of water aggregates in the interface layer.