The hydrothermal decomposition of dihydroxyacetone (DHA) is investigated under subcritical water conditions between 493 and 553 K at 200 bar using inicrotubular and pilot-scale flow reactors. The product samples contained a mixture of low molecular weight acids and aldehydes, such as glyceraldehyde, glycolic acid, lactic acid, acetic acid, and methylglyoxal. Quantification of products accounted for all the input carbon, within 95 +/- 5% between 493 and 533 K. A thermodynamically consistent kinetic model using thermodynamics of species derived from static electronic structure computational methods and rate parameters obtained from experimental data at initial stages of DHA decomposition is developed. The reaction pathway for DHA decomposition involves isomerization producing glyceraldehyde; dehydration to methylglyoxal; fragmentation to glycolic acid; and further decomposition of methylglyoxal to lactic acid, which becomes relevant at 553 K. The DHA product speciation is kinetically, rather than thermodynamically, controlled.