In this work, tunable optical properties of graphene quantum dots (GQDs) were achieved by centrifugation method. GQDs prepared through intercalating and exfoliating commercially available stacked graphene nanofibers were separated into two samples with different mean sizes by centrifugation. The separated GQD samples were characterized by transmission electron microscope (TEM). The optical properties of the GQD samples were measured by UV-visible and photoluminescence spectroscopy. The characterization results demonstrated that the UV and photoluminescence of GQDs were highly correlated with their sizes and surface chemistry. As the diameters of GQDs reduced, the UV peaks of the GQD blue shift, and the photoluminescence of PL red shift, indicating that the centrifugation method can be used to efficiently achieve tunable optical properties from as-synthesized GQD.