Excited state proton transfer (ESPT) of 1-naphthol has been studied in a polymer (hydroxypropylcellulose, HPC)-surfactant (sodium dodecyl sulfate, SDS) aggregate. The ESPT process of 1-naphthol is drastically retarded in the HPC-SDS aggregate above the critical association concentration (cac). The cac of SDS for HPC is found to be 2 mM, which is much smaller than its cmc (8 mM). The time-resolved emission data indicate that at a low SDS concentration (< 8 mM) the decay of the neutral emission and the rise and decay of the anion emission are very different from those in SDS micelles. Above the cmc of SDS, 1-naphthol molecules are distributed between the HPC-SDS aggregate and free SDS micelles.