Reactivity Controlled Compression Ignition can be extended over a wide spectrum of fuels and is anticipated as a promising strategy in meeting current and future emission regulations. In this study, the effect of n-butanol addition on combustion characteristics and emissions in a reactivity controlled engine was investigated experimentally. Different ratios of butanol-diesel blends at different settings of EGR and premixed ratios were applied to a light duty diesel engine. The butanol-diesel blends were directly injected into the combustion chamber while gasoline was injected at the intake port. Combustion phasing was maintained at 2.7 °CA for all of test points by adjusting fuel injection timing. The results showed that start of combustion delayed by n-butanol addition, so direct injection timing should be retarded to keep constant the combustion phasing. By increasing n-butanol fraction in the mixture from 0% to 40%, the optimum value of premixed ratio has decreased from 85% to 70%. The addition of n-butanol has reduced CO emission while HC emission has increased due to higher latent heat of vaporization of the alcohol fuel. The incorporation of an EGR unit in the experimental setup has improved the engine's thermal efficiency but of little effect on the optimum premixed fuel ratio. © 2018