Background: Disulfiram (DSF) has shown promising activity against glioblastoma in preclinical studies and is more effective when combined with copper (Cu). Our previous phase I study established the maximum tolerated dose (MTD) of DSF when combined with adjuvant temozolomide (TMZ). This phase I/II study aims to establish the MTD when disulfiram and copper are combined with concurrent radiation therapy (RT) and TMZ for newly diagnosed glioblastoma and to explore preliminary efficacy. Methods: Eligible patients were treated with standard RT and TMZ plus escalating doses of DSF (250 mg - 375 mg PO QD) and Cu (2 mg PO TID), followed by adjuvant TMZ plus DSF (500 mg/day) and Cu. The time-to-event continual reassessment method (TITE-CRM) was used to continuously estimate the probability of dose-limiting toxicity (DLT) and to assign patients to doses with an estimated DLT probability of approximately 20% with a margin of 5%. Tumor mutations were evaluated with next-generation sequencing for all patients. Results: Eighteen glioblastoma patients were treated with the study therapy: 8 with DSF of 250 mg/day and 10 with 375 mg/day. Three DLTs were observed: 1 with 250 mg/day (grade 2 urinary incontinence and ataxia), and 2 with 375 mg/day (both grade 3 elevated liver enzymes). DSF had an estimated DLT probability of 10% (95% CI: 3-29%) at 250 mg/day, and 21% (95% CI: 7-42%) at 375 mg/day. After a median follow-up of 12.3 months, 1-year progression-free survival (PFS) was 57%, and 1-year overall survival (OS) was 69%. There was no significant difference in PFS/OS when stratified by DSF doses, surgical extent, or MGMT methylation status. However, glioblastomas with IDH1 (n = 6), BRAF (n = 2), or NF1 (n = 1) mutations had significantly better PFS and OS than those without the mutations: 1-year PFS: 100% vs 22%, respectively, p = 0.001; 1-year OS: 100% vs 42%, respectively, p = 0.006. Conclusions: The MTD of DSF with RT/TMZ/Cu for glioblastoma is 375 mg/day, and the recommended phase II dose is 250 mg/day. Although confirmation with larger sample size is needed, the combination demonstrates promising preliminary efficacy for the subset of glioblastoma with IDH1, BRAF, and NF1 mutations. Clinical trial information: NCT02715609