Follow-up efficacy evaluation of stereotactic radiotherapy (SRT) helps to provide individualized treatment for intracranial tumors. However, biological changes at cytological level happen earlier than structural MRI can detect. Tissue sodium concentration (TSC) is sensitive to changes of tissue metabolic state and cell membrane integrity. In this study, we used sodium MRI at 7T to noninvasively quantify TSC and monitor the evolution of intracranial tumors after SRT. The results demonstrated that quantitative sodium MRI at 7T can reflect the efficacy of SRT, predict the volume change of tumor, and has the potential of finding the relapse of tumors in early stage.