The treatment of ovarian cancer has traditionally been intractable, and required novel approaches to improve therapeutic efficiency. This paper reports that thio-glucose bound gold nanoparticles (Glu-GNPs) can be used as a sensitizer to enhance ovarian cancer radiotherapy. The human ovarian cancer cells, SK-OV-3, were treated by gold nanoparticles (GNPs) alone, irradiation alone, or GNPs in addition to irradiation. Cell uptake was assayed using inductively coupled plasma atomic emission spectroscopy (ICP-AES), while cytotoxicity induced by radiotherapy was measured using both 3-(4,5)-dimethylthiahiazo (-z-y1)-3,5-di-phenytetrazoliumromide and clonogenic assays. The presence of reactive oxygen species (ROS) was determined using CM-H2-DCFDA confocal microscopy and cell apoptosis was determined by an Annexin V-FITC/propidium iodide (PI) kit with flow cytometry. The cells treated by Glu-GNPs resulted in an approximate 31% increase in nanoparticle uptake compared to naked GNPs (p < 0.005). Compared to the irradiation alone treatment, the intracellular uptake of Glu-GNPs resulted in increased inhibition of cell proliferation by 30.48% for 90 kVp and 26.88% for 6 MV irradiation. The interaction of x-ray radiation with GNPs induced elevated levels of ROS production, which is one of the mechanisms by which GNPs can enhance radiotherapy on ovarian cancer.