This paper presents the structural stability of patatin, the major potato (Solanum tuberosum cv. Bintje) tuber protein. Using far- and near-ultraviolet circular dichroism and fluorescence spectroscopy, the conformation of patatin was studied under various conditions as a function of temperature. Patatin is a protein that unfolds partly due to either heat or acid treatments. When the protein is highly structured at the start of a heat treatment (near-neutral pH), an apparent two-state thermal unfolding is observed. At low pH, when the starting conformation is already irreversibly unfolded to a certain extent, only minor changes occur upon heating. The residual structures could be part of one or more relatively stable domains. The acidic and the thermal unfolding appear to be similar, but are not identical. These results could contribute to an improved method of isolation, enabling novel food applications of potato proteins.