Nowadays, alcohol fuels are of increasing interest as alternative transportation biofuels even in compression ignition engines because they are oxygenated and producible in a sustainable way. In this paper, the experimental research activity was conducted on a single cylinder research engine provided with a modern architecture and properly modified in a dual-fuel (DF) configuration. Looking at ethanol the as one of the future environmental friendly biofuels experimental campaign was aimed to evaluate in detail the effect of the use of the ethanol as port injected fuel in diesel engine on the size, morphology, reactivity and chemical features of the exhaust emitted soot particles.The engine tests were chosen properly in order to represent actual working conditions of an automotive light-duty diesel engine. A proper engine Dual-Fuel calibration was set-up respecting prefixed limits on in-cylinder peak firing pressure, cylinder pressure rise, fuel efficiency and gaseous emissions.After the engine pre-calibration work, advanced instrument and diagnostic tools were installed and employed for on-line soot particle characterization. The morphological and chemical features of soot particles were studied in dependence of the ethanol-diesel substitution rate by analyzing the soot collected at the engine exhaust. Soot particles were sampled on Teflon filters, washed with dicloromethane to remove fuel residuals and characterized in terms of surface functionalization (infrared spectroscopy, FTIR), thermal resistance (thermogravimetry, TG) and optical properties (UV-Visible spectroscopy).Results indicated a negligible impact of ethanol premixed charge on the quality of the emitted soot. Ethanol is very effective in smoke reduction and has the potential to reduce the number and concentration of the emitted particles in the area of interest in terms of regulated emitted particles. Concerning the gaseous emissions, NOx emissions are controlled by EGR also in the DF operating mode. A general increase of CO and HCs is confirmed at lower loads, while the fuel efficiency tends to improve predominantly from medium to high loads.