In this work, novel ionic liquid 1-sulfopyridinium chloride {[Pyridine-SO3H]Cl} is synthesized, and characterized by IR, H-1 and C-13 NMR, UV as well as mass spectra. The ionic liquid is used as an efficient, homogeneous and reusable catalyst for the synthesis of 4,4'-(arylmethylene)-bis(3-methyl-1-phenyl-1H-pyrazol-5-ol)s by tandem Knoevenagel-Michael reaction of 3-methyl-1-phenyl-1H-pyrazol-5(4H)-one with various aromatic and hetero-aromatic aldehydes under mild reaction conditions. (C) 2013 Elsevier B.V. All rights reserved.