The hydrothermal conversion of organic wastes into more valuable substances using subcritical or supercritical water without oxidants has been investigated [6]. This study examines the hydrothermal decomposition of Baker's yeast cells, used as a model for spent Brewer's yeast waste,into protein and amino acids. The reaction was carried out in a closed batch reactor at various temperatures between 100 and 250 °C to determine the effect of temperature and hydrolysis time on the amount of residual yeast, TOC, and protein and amino acid in the soluble products.