In this study, the effects of the fusel oil on combustion and performance characteristics of an HCCI engine were examined comparatively with reference fuels. 37.5% fusel oil and 62.5% n-heptane were blended (Fusel40). RON40 used as reference fuel and to obtain the same octane number. Experiments were carried out at a fix intake air temperature of 350 K. Engine operation, BSFC, exhaust emission, CA50 and ITE maps were created as well as cylinder pressure and heat release rate traces by sweeping lambda between the misfire and knock limits at each engine speed at three different compression ratios of 11, 12 and 13. Despite its lower heating value, Fusel40 did not lead performance loss for the HCCI engine. Moreover, Fusel40 provided higher brake torque due to better location of the SOC and CA50 at a compression ratio of 13 and minimum BSFC was obtained as 228.6 g/kWh with Fusel40. The maximum ITE was obtained as 44.6% at a compression ratio of 12 and lambda of 2.9 with RON40 fuel. On the other hand, Fusel40 provided higher thermal efficiency than RON40 for a wide operation range of the HCCI engine. ITE ranged between 30 and 43 % for Fusel40 while it was 26-44% for RON40. It is also found that increasing the compression ratio of HCCI engine alone couldn't be improved thermal efficiency without the start of combustion and combustion phase control. It was determined that fusel oil has a better influence to reduce CO and HC emissions than increasing the compression ratio.