Keggin-type polyoxometalate (POM) nanoparticles based on [PW12O40](3-) and [SiW12O40](4-) with Ag+ and (ZrO)(2+) cations were prepared under ultrasound irradiation. The results of SEM and XRD revealed the average size of particles in the range of 24-95 nm. The moles of crystallization water per mole of nanocatalysts were in the range of 3-9. EDX spectra confirmed the successful replacement of protons of H3PW12O40 and H4SiW12O40 with Ag+ and (ZrO)(2+) cations. These nanoparticles were used as heterogeneous catalysts for the synthesis of a poly (amido-ester) at room temperature. All polymers were fully characterized. Although employing the nanocatalyst resulted in at least 22% improvement in the polymerization yield but decreased the molecular weight of the polymers due to their restrictive effect on the mobility of reactive groups at the end of growing chains. (C) 2017 Elsevier B.V. All rights reserved.