Silica sulfuric acid as an efficient and reusable heterogeneous catalyst have been used for the preparation of 2H-indazolo[2,1-b]phthalazine-1,6,11(13H)-trione derivatives from the three-component condensation reaction of phthalhydrazide, dimedone, and aromatic aldehydes under solvent-free conditions in good to excellent yields and short reaction times. (C) 2008 Elsevier B.V. All rights reserved.