The optical properties of quantum dots (QDs) are altered by exposure to air and light; upon such exposure, the quantum yield is typically reduced. Improved understanding of surface oxidation and oxide-layer behavior, both of which influence the photoluminescence of QDs, is necessary for advancing the use of QDs. In this study, the oxide layer properties of QDs are investigated. The QDs are synthesized and subsequently oxidized by heat treatment in atmospheric conditions, and the luminescence properties of the resultant QDs are investigated. The emission properties of QDs are characterized by photoluminescence. The composition and bonding structure of oxidized CdSe QDs are investigated by X-ray photoelectron spectroscopy (XPS). The XRD peaks of oxidized CdSe QDs match CdSe and CdO peaks. CdO is formed by partial oxidation of CdSe QDs. Transmission electron microscopy (TEM) image is confirmed morphology of oxidation before and after of CdSe QDs.