The process of silver ions reduction in CF₃COOAg — Qr — EA system where Qr is quercetin, EA — ethyl acetate in the presence of polyethylene glycol (PEG). Polyethylene glycol with molecular weight of 1500 amu and 6000 amu has been used in the work. Various amounts of polyethylene glycol of different molecular weight have been introduced into the solutions of reagents prior to redox reaction and at various time intervals after its beginning. The absorbance change in the spectral band maximum fallen into the absorption of colloidal element silver particles formed in the course of the reaction have been recorded. The effect of stabilizer on the reaction has been estimated in terms of dependencies course change A = f (t). As a result it has been found that the introduction of polyethylene glycol leads to slowing of the redox reaction. Decrease in speed of silver ions (I) reduction is associated with the predominance of complexation of PEG with silver trifluoroacetate and with diffuse factor at molecular weight and stabilizer concentration encrease.