The heat shock protein， Hsp60， is one of the most abundant proteins in . Given its sequence homology to the Hsp60 or GroEL， Hsp60 from would be expected to function as a molecular chaperone in this organism. is an organism that grows on the gastric epithelium， where the pH can fluctuate between neutral and 4.5 and the intracellular pH can be as low as 5.0. This study was performed to test the ability of Hsp60 from to function as a molecular chaperone under mildly acidic conditions. We report here that Hsp60 could suppress the acid-induced aggregation of alcohol dehydrogenase (ADH) in the 7.0-5.0 pH range. Hsp60 was found to undergo a conformational change within this pH range. It was also found that exposure of hydrophobic surfaces of Hsp60 is significant and that their exposure is increased under acidic conditions. Although， alcohol dehydrogenase does not contain exposed hydrophobic surfaces， we found that their exposure is triggered at low pH. Our results demonstrate that Hsp60 from can function as a molecular chaperone under acidic conditions and that the interaction between Hsp60 and other proteins may be mediated by hydrophobic interactions.