Abstract: Scanning electron microcopy (SEM) and differential scan calorimetry (DSC) were used to evaluate structure changes in Saccharomyces cerevisiae cells under the treatment of high-pressure CO₂ over the fermentation broth. Compared with controlled fermentation, the ethanol concentration in the fermentation broth after 24 h greatly decreased under high-pressure CO₂. DSC studies of whole cells showed that the ribosomes and DNA were not changed after high pressure CO₂ treatment although some components were denatured,leading to the lowering of the corresponding decomposition temperature. The fermentation under 1 and 8 MPa CO₂ caused obvious changes on the wall surface of cells.Wrinkles were formed on the wall of cells and the cell wall coarseness increased at elevated pressure as observed with SEM observations.