This investigation used a packed-bed reactor filled with coated titanium dioxide glass beads which was activated by a 365 nn UV light for heterogeneous photocatalytic decomposition of trichloroethylene under different conditions of flowrate, oxygen content, moisture and light intensity. For the flowrate of feed gas between 100-500 mL/min, the reaction rates increased with an increasing flowrate below 300 mL/min. When the flowrate was more than 300 mL/min, the reaction rate was not affected by the flowrate. For the oxygen content in the range of 0-20 %(v/v), it indicated that under 10 %(v/v) oxygen content the reaction rate increased as the oxygen content increased. The increase of moisture content lowered the reaction rates in the range of 230-30000 ppmv. The reaction rate of 6 mu M TCE increased as the light intensity increased, and was proportional to the 0.61 order of the light intensity. The deactivation of the TiO2 described in the literature was not observed in this study. (C) 1998 Elsevier Science Ltd. All rights reserved.