Quantitative detection of glucose is an important issue in food industry, various biotechnological processes and medication of metabolic disorders. Many ways have been developed to approach this target. In this study, we demonstrated a simple assay system containing glucose oxidase (GOD) and CdSe/ZnS quantum dots (QDs) for specific and quantitative detection of glucose. The role of QDs functioned as an "indicator" to reveal the acidity change of the assay system resulting from the enzymatic oxidation of glucose. By controlling the initial buffer conditions of the assay system at 10 mM or 30 mM phosphate, pH 8.0, the quench ratio of PL intensity of QDs at 586 nm was found to be linear to the tested glucose in the range of 0.2-10 mM or 2-30 mM, respectively. The assay system also provides a convenient way to determine the glucose concentration by visualizing the color change of QDs fluorescence. As compare to most of the existing methods, this newly developed system possesses many advantages, including simplicity, low cost, high flexibility, and good sensitivity. Furthermore, no complicated chemical modification and enzyme immobilization were needed in this system.