Influence of hydrocarbon structure on selective reduction of NO by hydrocarbons (HC-SCR) over Cu-Al2O3 catalyst was studied by using linear and branched alkanes with different carbon numbers. As the carbon number of linear alkanes increased, reaction rates of NO and hydrocarbon increased. Reaction rates of NO and hydrocarbon for branched alkanes were lower than for linear alkanes of the same carbon number. Structure of hydrocarbon had no influence on the selectivity. Both reaction rates of NO and hydrocarbon had good correlations with mean bond energy of the alkanes. These correlations were also confirmed for the other catalysts such as Ag-Al2O3, Cu-MFI and so on, indicating that the mean bond energy of a hydrocarbon is a useful parameter to estimate its ability as a NO reductant for HC-SCR in diesel emission containing various hydrocarbons.