In this experimental work, the influence of some bio-fuels on the spark-ignition engine combustion efficiency and engine-out emissions was investigated. A conventional 1.6 l port injection engine was tested over steady-states, with some bio-ethanol/gasoline blends (0, 10, 20, 30, and 85 vol% of ethanol in gasoline) and with a 10 vol% of n-butanol in gasoline. Study of combustion development was made through the heat release analysis of pressure cycles measured in combustion chamber. Regulated emissions, unregulated organics (Polycyclic Aromatic Hydrocarbons, carbonyl compounds and Volatile Organic Compounds) and particulate were measured. Particulate was characterized in terms of total particle number (PN) and size distribution between 7 nm up to 10 lm. The tests were carried out at stoichiometric conditions in closed loop and spark advance was optimized with a calibration tool software in order to have the same peak pressure position. By fueling the alcohol blends, the engine-out particulate emissions are strongly reduced compared to gasoline. The PN reduction percentage ranges between 60% and 90%. The benefits also concern some gaseous unregulated species very harmful for humans, such as benzene and benzo(a)pyrene (reduction of almost 50% and 70% respectively). The highest oxygen content of alcohol blends, instead, provides an increasing of the total carbonylic emissions.