The present invention relates to use of nuclear protein 1 (NUPR1) in diagnosing and treating brain tumors and, more particularly, to a biomarker composition comprising NUPR1 for diagnosing brain tumors or for predicting prognosis and a composition comprising an NUPR1 inhibitor for preventing or treating brain tumors. The level of NUPR1, particularly NUPR1 isoform A, according to the present invention is significantly increased in patients with brain tumors and further remarkably in patients with malignant brain tumors of poor prognosis, compared to healthy normal persons, so that NUPR1 can be used as a biomarker for diagnosis of brain tumors or for prediction of prognosis. In addition, NUPR1, particularly NUPR1 isoform A according to the present invention can be used as a target for brain tumor treatment and also, in future, in screening a therapeutic agent for brain tumors as the inhibition thereof can suppress the growth, metastasis and invasion of brain tumors.