This research utilizes corncob waste for making bioethanol by RON 109. The objective of this research is to get the best performace of exhaust emission by mixing gasoline RON 90 from E5, E10, E15, E20, to E25, and 10:1, 11:1 and 12:1 of compression ratio. In addition, the control variable covered 1400 rpm, 2400 rpm, and 3400 rpm engine speed. The testing data of exhaust emission was taken only on the carbon monoxide (CO) and hydrocarbon (HC). The result on this biethanol from corncob waste showed that the lowest exhaust emission on carbon monoxide and hydrocarbon and recom mended to be used was found on E10 fuels at 10:1 compression ratio, and E20 fuels at 11:1 compression ratio. The result obtained from this research demonstrated that the carbon monoxide and hydrocarbon emissions that produced by corncob waste bioethanol were environmently friendly compared to gasoline use only (E0).