Decomposition of N2O in the temperature range 200-500degreesC was studied on catalysts composed of rhodium supported on gamma-Al2O3 doped with different amounts of Li, Na, K, Cs cations. It has been found that doping with alkali metals influences the dispersion of rhodium which is reflected in the changes of catalytic activity. Dependence of activity on dispersion is linear for potassium and cesium, whereas in the case of sodium a dramatic decrease of activity is observed when the concentration of sodium surpasses 0.07-0.08 mol% due to the modification of the number or specific activity of active sites. The detrimental effect of sodium may be compensated by doping with potassium. (C) 2004 Elsevier B.V. All rights reserved.