Glioblastoma (GBM) is the main form of primary brain malignancies with a dismal prognosis partly due to its invasive growth and rapid relapse. GBM frequently developed resistance to current standard-of-care therapeutic modalities, including surgery, radiation and chemotherapy, of which temozolomide (TMZ) is the most widely used first-line anti-GBM drug. Despite the intense efforts of the past decades, the underlying mechanisms of GBM resistance to TMZ remain largely unclear. Here we show that the long noncoding RNA (lncRNA) PSMG3-AS1 is significantly upregulated in GBM and its expression correlates with the grade of glioma, with the highest level observed in GBM (Grade IV glioma). We also demonstrated that PSMG3-AS1 mediates the resistance of GBM to TMZ, as knockdown of PSMG3-AS1 remarkably increased the sensitivity whereas overexpression of PSMG3-AS1 in sensitive GBM cell line induced a resistance phenotype to TMZ. Mechanistically, PSMG3-AS1 directly binds to c-Myc and thus stabilizes c-Myc in the nucleus to promote the survival of GBM cells under treatment of TMZ. Our data demonstrated an unreported role of PSMG3-AS1 in TMZ resistance and provide a potential novel target to tackle TMZ resistance in GBM.