The catalytic decomposition of N2O (28 mol%) has been studied for the Ru/Al2O3 system with various ruthenium contents (Ru wt% = 0.00-0.26). The optimized catalyst of the studied system has a high catalytic activity of 4.8 x 10(4) mu mol (N2O) g(-1) h(-1) at 400 degrees C. The study shows that the surface area of Ru/Al2O3 decreases with increase of loading of the metal. Two different types of surface structure are formed, and the optimized catalyst is found in the intermediate region between them. The catalyst has been investigated further with various background gases (O-2, CO2, and H2O). It is found that O-2 has little inhibitive effect on the high conversion rate reaction while it shows a certain effect at low conversion (low temperature). Acidity-basicity of the catalyst has been examined with the probe gas CO2. In contrast to CO2, which does not adsorb on the catalyst, water shows a strong tendency to hamper the decomposition. The reaction on the optimized catalyst can be described as first order with respect to N2O partial pressure. Using the findings of this work, a two-step process has been proposed for the adipic acid off-gas treatment.