Fig. 1 shows CO, HC and NOX emissions for one entire cycle. We can see that CO emissions for base and E10 test fuels were 6.85 and 4.74 g/km. Namely, COemission amount was decreased by about 30.8% for E10 fuel, compared to base fuel. This is due to improving the combustion process as a result of the oxygen content in ethanol fuels. From Fig. 1(b), it was observed that HC emission was 0.562 g/km, if motorcycle engine was fueled with unleaded gasoline, whereas HC emission was 0.384 g/km for blended ethanol fuel. This indicated the HC emission was reduced by nearly 31.7% for one whole cycle. This result can be also explained by the fact that oxygenated characteristic of ethanol in blend fuels is more effective in enhancing oxidation of hydrocarbons than that in air. NOX emissions for one entire cycle were presented in Fig. 1(c). For base and E10 fuels, NOX emission values were 0.368 and 0.345 g/km, respectively. The reduction of NOX emissions was relatively smaller, about 5.9% for E10 fuel. In other words, the ethanol added to gasoline produces minor effect on the decrease of NOX emissions.