Decomposition of glycine was investigated in the temperature range of 260 to 340degreesC and at constant pressure of 30 MPa. Amines, organic and carbonic acids were obtained as major products. Based on these products, glycine decomposition under hydrothermal conditions is speculated to take two main paths, (i.e. decarboxylation to produce ammonia and organic acids, and deamination to produce carbonic acid and methylamine). The overall decomposition rate of glycine was found to be of the first order with respect to glycine concentration within the range of experimental conditions. These results are important as basic information in understanding the behavior of amino acid production from protein using high temperature and high pressure water.