ABSTRACT A simple and efficient procedure for synthesis of 4,4′-(arylmethylene)bis(1H-pyrazol-5-ols) by one-pot three-component condensation of aromatic aldehydes, ethyl acetoacetate, and phenylhydrazine/hydrazine hydrate under solvent-free conditions in the presence of [Et 3 NH][HSO 4 ] as catalyst is described. The present protocol offers several advantages such as using a reusable and cost-effective ionic liquid, high yields, simple procedure, easy work-up and eco-friendly reaction conditions. Keywords : 4,4′-(Arylmethylene)bis(1H-pyrazol-5-ols); [Et 3 NH][HSO 4 ]; Solvent-free; Multicomponent reaction INTRODUCTION 4,4′-(Arylmethylene)bis(1H-pyrazol-5-ols) are applied as fungicides 1 , pesticides 2 and dyestuffs 3 . The condensation of aldehydes with two equivalents of 3-methyl-1-phenyl-5- pyrazolone is a conventional chemical approach to 4,4′-(arylmethylene)bis(1H-pyrazol-5-ols). Many catalysts have been used for this transformation such as xanthan sulfuric acid 4 , phosphomolybdic acid