A novel approach to the synthesis of 3,4-dicarbonyl-substituted pyrazoles from a wide range of 1,3-dicarbonyl compounds and oxamic acid thiohydrazides was developed via iodine-promoted cascade imination/halogenation/cyclization/ring contraction reaction accompanied by sulfur elimination. This procedure provides a highly efficient and facile route to functionalized pyrazoles from readily available substrates under mild reaction conditions.