The role of ethanol, as substituent to ethylene, on the formation of particulate matter has been investigated in different flame configurations by using in situ optical techniques. Laser induced fluorescence and incandescence signals, correlated to small precursor nanoparticles and large soot particles, respectively, have been measured in premixed and counter-flow diffusion flames of ethylene doped with different amounts of ethanol, covering a wide range of ethanol addition, much higher than that reported in the literature. In premixed flames, the addition of ethanol reduces nanoparticle and soot particle formation. The effect is stronger for the soot particles, that is, particles with sizes larger than 10 nm, and in flames operated close to the soot threshold limit. The addition of 30% of ethanol reduces soot particle concentration below the detection limit, whereas nanoparticles are still formed in large amounts. The counter-flow diffusion flame configuration shows a different behavior. In the fuel side of the flame, a noticeable increase of both nanoparticle and soot particle concentrations is detected for amounts of ethanol added up to 20 vol %, whereas a decrease of the particulate formation, both nanoparticles and. soot, is observed for larger amounts of ethanol added. Conversely, in the oxidizer side of the flame, particulate matter is always reduced when ethanol is added to the fuel. The results show that the role of ethanol in the formation of nanoparticles and soot is not always in the sense of reduction, but it also strongly depends on the combustion conditions.