Gasoline used in an Otto engine can be substituted by pure Bioethanol or Gasoline-Bioethanol blends. The engine performance can be affected by the mixture. Specifically, the blends can affect (Increasing or decreasing) power, torque, and emission produced by the engine. It is caused by the different characteristic of the Gasoline-Bioethanol blends depending on the volume percentage of the Bioethanol. Theoretically, as the increasing of the volume percentage of Bioethanol to the mixture, the power and torque produced would be decreased because of the lower energy contained rather than gasoline. As a biofuel, Bioethanol is a natural product and created by the fermentation of plants containing sugar and starch which has a similar physical and chemical characteristic to gasoline. The objective of this experiment was to determine the effect of Bioethanol-gasoline blended fuels on the performance of an engine. In this case, the performance includes specific fuel consumption, power, and torque. The experimental test was using gasoline with octane number 88, 92, 98, and 30%, 40% Bioethanol blend. The effect carried out by increasing the volume number of Bioethanol to the gasoline is the increasing of the power and torque produced by the engine. Keywords: Gasoline, bioethanol, research octane number, engine performance.