This paper presents a first structural characterization of isolated patatin, the major potato tuber protein, at ambient and elevated temperatures. Isolated patatin at room temperature is a highly structured molecule at both secondary and tertiary levels. It is estimated from far-ultraviolet circular dichroism data that about 33% of the residues adopts an α-helical and 46% a β-stranded structure. Patatin is thermally destabilized at temperatures exceeding 28°C, as was indicated by near-ultraviolet circular dichroism. It was shown that parts of the α-helical contributions unfold in the 45-55°C region, whereas the β-stranded parts unfold more gradually at temperatures of 50-90°C. This was confirmed with Fourier-transform infrared spectroscopy. Differential scanning calorimetry indicated a cooperative transition between 50-60°C, most likely reflecting the unfolding of α-helical parts of the molecule. Furthermore, fluorescence spectroscopy confirmed a global unfolding of the protein between 45-55°C. The observed unfolding of the protein coincides with the inactivation of the patatin enzyme activity and with the precipitation as occurs in the potato fruit juice upon heating. At high temperatures, patatin still contains some helical and stranded structures. Upon cooling the protein partly refolds, it was observed that mainly α-helical structures were formed.