The addition of ethanol to gasoline decreases the heating value and increases the octane number of the fuel mixture, thus influencing the increase in torque and fuel consumption of the engine. However, it is not yet clear of how much increase in torque and fuel consumption of the engine by using mixtures of gasoline-ethanol fuel that use a low-octane number of gasoline base fuel compared to a high-octane number of gasoline base fuel. In this study, we test the performance of a 150cc motorcycle engine (without any modification on engine and fuel injection system) with varies of fuels consists of gasoline RON 88, gasoline RON 98, gasoline RON 88 + 10% ethanol (88 E10), and RON 98 + 10% ethanol gasoline (98 E10) on AVL dynamometer testing facility. Based on data collected from the test, the parameters of power, torque, SFC and AFR were analyzed to determine the effect of adding 10% ethanol to the gasoline RON 88 base fuel compared to gasoline RON 98 base fuel to the engine performance. From the results of this study, it is known that the engine performance with the use of 98 E10 fuel is better than 88 E10 (higher power and torque, and generally lower SFC).