To provide a water-soluble catalyst capable of dissociating a blocking agent at low temperature in an aqueous system, and applications thereof.

Provided are a catalyst for low-temperature dissociation of a blocking agent containing a β-diketone and a metal compound including a hydrophilicity-imparting group as a ligand, an aqueous emulsion solution containing the catalyst for low-temperature dissociation of a blocking agent and a blocked isocyanate, and an aqueous one pack-type thermosetting composition containing the catalyst for low-temperature dissociation of a blocking agent, the blocked isocyanate, and a compound having an isocyanate-reactive group.