This research presents a practical “green” method to obtain lactose-capped colloidal zinc selenide quantum dots in an aqueous medium at a low temperature. Obtained samples with sodium selenosulfate solution being a source of selenium ions and zinc chloride being a source of zinc ions have been studied with atomic force microscope. The spherical shape of nanoparticles has been revealed, and the characteristic dimension of semiconductor nanoparticles aggregated formations has been obtained. Infrared spectral analysis proves the presence of lactose on a surface of zinc selenide quantum dots. The quantum dots demonstrate the presence of quantum size effect and sufficiently large surface energy. This fact explains that the quantum dots of the obtained semiconductor possess unique electronic and optical properties and can be used in practice in areas, such as nano optronics, nano electronics. Lactose absorbed on a surface of nanoparticles allows a possible scope of implementation to be expanded to areas of biology and medicine. For example, they can be used as biomarkers.