Abstarct: We have described one-pot solvent-free rapid and efficient method for the synthesis of 1H-pyrazolo[1,2-b]phthalazine-5,10-dione derivatives via the silica sulfuric acid catalyzed reaction of aldehyde, malononitrile, and phthalhydrazide at 120 °C. The simplicity of the system, ease of separation and reuse of the catalyst and ease of work-up make the described method for the synthesis of 1H-pyrazolo[1,2-b]Phthalazine-5,10-dione an attractive, which can be extended to the synthesis of other heterocyclic compounds.