Coacervation presents a way how to produce organic-inorganic hybrid materials from unusual precursor mixtures. In the present work, water-based sodium metaphosphate-poly(ethylene glycol) (NaPO 3 -PEG) coacervates were analyzed using a quartz crystal microbalance with dissipation monitoring (QCM-D). The frequency and dissipation shifts were used to calculate the storage and shear loss moduli for all mixtures. The effect of PEG concentration and molar mass in parent solutions on viscoelasticity was evaluated. This, coupled with analysis of the parent NaPO 3(aq) and PEG (aq) solutions, shed light on the coacervation phenomenon for this system. The results show that the PEG (aq) solutions with molar masses >1000 g mol -1 exhibit elastic behavior linked to structural changes in PEG chains. At sufficiently high PEG content and NaPO 3 concentration, a collapsed state of PEG chains in the coacervate was observed.