Mg(HSO4)2 is an efficient, readily available, and eco-friendly catalyst for the synthesis of 1,3,5-trisubstituted or 1,3,4,5-tetrasubstituted pyrazoles via the condensation of 1,3-diketones and hydrazine. Mild condition, simplicity of procedure, high yields, easy work-up and short reaction time are some advantages of this green protocol.