Among many techniques used for increasing fuel efficiency of a modern Gasoline Direct-Injected (GDI) engine are boosting and stratified operation. In modern downsized GDI engines, boosting is standard in order to achieve a high power output. Boosted GDI-engines have however mostly been operated in homogenous mode and little is known on the effects of operating a boosted GDI-engine in stratified mode.This paper presents the influence on combustion, standard emissions and particulate size distribution in a Spray-Guided, Gasoline, Direct-Injected (SGDI), single cylinder, research engine operated with various levels of boost.The engine was operated in steady state mode at five engine operating points of various load and speed. The engine was boosted with a Roots blower and operated at four levels of boost as well as atmospheric pressure for comparison. The engine was fueled with market gasoline (95 RON) blended with 10% ethanol. The gas motion induced by the engine head was primarily tumble motion but a small amount of swirl. The spark plug and injector was mounted in parallel with the intake valves.Results indicate that exhaust temperature and NOx emissions decrease with increasing boost. Hydrocarbon emissions increase with increasing boost. The results on particulate emissions indicate that nucleation mode particulates increase with increasing boost. The opposite trend was observed for agglomeration mode particulates which decreased with increasing boost pressure.