Decomposition reaction of water-containing nitrous oxide has been carried out in a tubular quartz reactor with GC on low-metal content Ru/Al2O3 catalyst (Ru 0.2 wt.%). Activation parameters of catalyst have been examined and two processes have been established using dry or wet N2O (27-31 mol%) feed gases. After activation, N2O can be decomposed in water vapour (up to 3 mol%) under optimal operational conditions. It is found that the effect of water is non-linear, and it can be significantly reduced at high operating temperature. The rate law of N2O decomposition in wet environment can be expressed as first order to partial pressure of nitrous oxide with an averaged apparent activation energy of 139 kJ/mol. Chemical composition, surface area and crystallographic structure of catalyst have been investigated with ICP/BET/XRD/FTIR. The studied catalysts are both chemically and hydrothermally stable. High conversion activity [1.2x10(2) mmol (N2O)/g.h at 470.5 degrees C (GHSV=14400 h(-1), N2O=29.9 mol%, H2O=3.0 mol%, balanced with He)] has been found and an operational process of the catalyst has also been proposed.