The present invention relates to a pharmaceutical composition for elevating radiation-sensitivity of cancer cells, which comprises: a nanoparticle containing with a first element, which is iron, copper, or the combination thereof; and a pharmaceutically acceptable carrier, wherein the nanoparticle is a metal nanoparticle, an alloy nanoparticle, or a metal nanoparticle with core-shell structure, and the size of the nanoparticle is under a controllable range of 3 nm to 150 nm. In addition, the present invention provides a detection method to detect radiation-sensitivity of the cancer cells through different modalities such as CT or MRI due to its native high CT number and magnetic property. Furthermore, the present invention provides a pharmaceutical composition for elevating radiation-sensitivity of the cancer cells through preferential uptake of the nanoparticle, in order to enhance the radiation-sensitivity of the cancer cells and improve the efficiency of radiation therapy to the cancer cells.