The objective of this work was to investigate the mechanism of the inhibition of aggregation of petroleum asphaltenes using new ionic liquids (IL). The ionic liquids conjugate a good solubility in nonpolar environment with strong electron donor-acceptor properties. In this study, 1-propyl boronic acid-3-alkylimidazolium bromides and 1-propenyl-3-alkylimidazolium bromides were tested. A lateral chain containing either the boronic acid or the propenyl moiety was substituted for the classical 1-methyl-3-alkylimidazolium bromide. The boronic acid is a weak acid but a very efficient Lewis acid. It was demonstrated that the presence of the boronic acid moiety enhances interactions between asphaltenes and ionic liquids and limits considerably asphaltene aggregation. The length of the side alkyl chain of the ionic liquid is an important parameter also. The minimum length of eight carbons was necessary to obtain sterical stabilization of IL-asphaltene complexes.