A method was developed to synthesize a nanosheet at the interface of an aqueous layer of Pd-II ions and an aqueous layer of hydrophilic polymer bearing a metal coordination unit (HPMC). The nanosheet was synthesized through generation of an interface by the addition of an aqueous solution of Pd-II ions with a low specific gravity (1.03 g/cm(3)) to a dispersed aqueous solution of HPMC with a high specific gravity (1.50 g/cm(3)), resulting in rapid cross-linkin at the interface. An electron probe microanalysis mapping image showed that the Pd-II ions were uniformly dispersed in the nanosheet. The nanosheet showed a high catalyst activity for the Mizoroki-Heck cross-coupling reaction with a turnover number (TON) and turnover frequency (TOF) greater than 3,333,333 and 138,889 h(-1), respectively. These are the greatest TON and TOF values reported for heterogeneous polymeric catalysts for the Mizoroki-Heck reaction.