A series of new carboxyl-functionalized benzimidazolium based ionic liquids (CFBILs) were synthesized and characterized by FT-IR, NMR and HR-MS (EI). Catalytic activities of CFBILs were evaluated towards the solvent free, one-pot synthesis of 1-amidoalkyl naphthol derivatives and found comparable to those of imidazolium based ionic liquids. Hammett values (H0) of the synthesized CFBILs have been determined using UV-vis spectroscopy and correlated with their catalytic activity. The catalytic activities were found to increase with the acidity of the CFBILs which reveal the formation of hydrogen bonding of CFBILs with aldehydes and this could play a crucial role to facilitate the product formation. The catalyst has shown excellent stability over wide range of temperature and good recyclability for several runs. © 2013 Elsevier B.V. All rights reserved.