Polyoxometalates (POMs) have been found to be good end-capping ligands for gold nanoparticles (AuNPs). Herein, we introduce a new synthetic method to synthesize gold nanoparticle-POM hybrids by heating a solution of AuNO3(PMe3) in acetonitrile in the presence of appropriate POM species with tetrabutylammonium (TBA) as a countercation at 120 °C in a microwave. This method allowed us to produce POM-capped AuNPs without over-reduction of the solution causing decomposition or reorganization of the POMs. Analysis of the resulting material by transmission electron microscopy showed that the POM's size, charge, and functionality are key factors controlling the resulting POM-AuNP hybrid structure. Additionally, the reaction was monitored by electrospray ionization mass spectrometry (ESI-MS), ultraviolet-visible spectroscopy, and dynamic light scattering. The ESI-MS studies reveal crucial information regarding the nature of the reaction that takes place, showing the cation exchange between Au(I) and TBA cations, followed by self-reduction of the Me3PAu(I)-POM complex.