The UV-Visible spectroscopic features of tarry and solid carbon species produced in premixed flames burning aliphatic (ethylene, n-hexane, cyclohexane, n-heptane) and aromatic fuels (benzene) were investigated in terms of spectral shape and mass specific absorption coefficients. The spectral properties of dry soot showed significant changes as a function of the flame position and of C/O ratio. Moreover, some peculiarities of the soot spectral properties for the benzene flame were observed and related to the different internal structure of benzene soot in comparison with aliphatic soot structure. The mass specific absorption coefficient was found to be quite constant for the slighty-sooting flame along the flame axis, whereas it increased up to 5 times in heavily-sooting conditions, indicating a relevant effect of the C/O ratio and of the residence time on the aromatic structure of the soot.