The effect of glucose on fluorescence of synthesized ZnCdS nanoparticles in the presence of glucose oxidase or in a mixture of glucose oxidase and peroxidase has been investigated. Behavior of fluorescence characteristics of ZnCdS nanoparticles with nonstabilized surface and coated with polymer shell is compared. It has been shown that, for uncoated ZnCdS nanoparticles, hydrogen peroxide formed by glucose oxidation with glucose oxidase causes static quenching of the nanoparticle fluorescence. A quenching mechanism is proposed in which surface centers of fluorescence, which include cationic vacancies, trap oxygen ions supplied by hydrogen peroxide. It has been shown that the linear Stern–Volmer plot has no threshold within the investigated concentrations of glucose. The sensitivity of ZnCdS nanoparticles to glucose, determined from the slope of linear Stern–Volmer plot, is maximum for polymer-coated nanoparticles and is . With peroxidase, there is a threshold concentration of glucose (160 μM) below which the nanoparticles become insensitive to glucose.