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Abstract: Decomposition of 1,1,1-trichloroethane (TCA) in hot compressed water, with or without an oxidizer, was studied using an optically transparent anti-corrosive fused silica capillary reactor (FSCR), and Raman spectroscopy. The phase behavior of TCA in water during hydrolysis/oxidation was observed continuously under a microscope and recorded with a digital-camera/recording system, A new phase behavior of TCA was found in the presence of excess H2O2; TCA was first gasified during heating, followed by liquefaction under increasing internal pressure as a result of the formation of O2 from the decomposition of H2O2, and subsequently gasified again during further heating up to 400°C. The gaseous products of TCA oxidation in hot compressed water were monitored quantitatively and qualitatively using Raman spectroscopy. The effects of the operating parameters, namely the stoichiometric amount of oxidizer, temperature, and reaction time, were investigated. In our experiments, it was found that 100% CO2 yield was achieved with a 175% stoichiometric amount of H2O2 at 420°C after 360s. Temperature plays a key role in the decomposition of TCA and the formation of CO2 in the supercritical water oxidation (SCWO) process. Based on our results, a reaction mechanism for TCA decomposition in hot compressed water was proposed. The global reaction kinetics showed that the formation of CO2 in the SCWO of TCA was a first-order reaction. [Copyright &y& Elsevier]