Nowadays, the evaluation of waste products has gained importance. The fusel oil, which is obtained as a waste product in sugar factories, has a high proportion of isoamyl alcohol. Alcohols having a high-octane number give lower emission values when used as fuel. In this study, isoamyl alcohol was used at high compression ratio (CR) to improve performance and emissions in a spark ignition (SI) engine. The experiments were performed at full load, different CRs (8.0:1, 8.5:1 and 9.0:1) and different speeds (2600, 2800, 3000 and 3200 rpm) using different fuels A0 (%100 gasoline), A10 (%10 isoamyl alcohol-%90 gasoline), A20 (%20 isoamyl alcohol-%80 gasoline) and A30 (%30 isoamyl alcohol-%70 gasoline). According to the obtained results, exhaust emissions decreased with using of isoamyl alcohol compared the using of gasoline at all CRs. With the use of A30, carbon monoxide (CO), nitrogen oxides (NOx) and hydrocarbon (HC) emissions decreased by approximately 12.2%, 35.6% and 6.45%, respectively compared to gasoline. The cylinder gas pressures (CGP) and heat release rates (HRR) were recorded for each CR and fuel blend. Moreover, by increasing the CR, brake thermal efficiency (BTE) increased about 2.67% with A20 compared to gasoline on 9.0:1 CR. Furthermore, torque and effective power also increased by 2.03% and 2.51% with A20, respectively.