Ethanol is becoming more popular as a fuel component for spark-ignited engines. Ethanol can be used either as an octane enhancer of low RON gasoline or splash-blended with gasoline if a single injector is used for fuel injection. If two separate injectors are used, it is possible to inject gasoline and ethanol separately and the addition of ethanol can be varied on demand. In this study, the effect of the ethanol injection strategy on knock suppression was observed using a single cylinder engine equipped with two port fuel injectors dedicated to each side of the intake port and one direct injector. If the fuel is injected to only one side of the intake port, it is possible to form a stratified charge. The experiment was conducted under a compression ratio of 12.2 for various injection strategies. From the experimental results, it was found that injecting ethanol to the left side only of the intake port while both intake valves were open required approximately 52.1% (at 1500rpm) or 60.6% (at 2000rpm) less ethanol compared to the case in which ethanol is injected to both sides of intake port while intake valves are closed under a similar level of knock frequency. Furthermore, the engine load was maintained to the same level.