Abstract The treatment of primary central nervous system lymphoma (PCNSL) is currently limited by the impermeability of the blood-brain barrier. This study aims to assess the efficacy and safety of the R-MO regimen (rituximab, high-dose methotrexate, and orelabrutinib) in the treatment of patients with newly diagnosed PCNSL. A total of 37 patients were enrolled in this prospective, multi-center phase II trial. The post-induction overall response rate (ORR) was 90.3%, and the complete response rate (CRR) was 87.1%. Throughout the trial, the best ORR was 97.1%, and the best CRR was 94.1%. With a median follow-up of 12.6 months, the median progression-free survival (PFS) was not reached, with a 1-year PFS rate of 83.6%, meeting the primary study endpoint. The 1-year overall survival rate was 89.6%. Notably, there was no significant difference in PFS between transplanted and non-transplanted groups (P = 0.226). The most common adverse events were neutropenia, lymphocytopenia, and infections, each occurring in 45.9% of patients. Overall, the addition of orelabrutinib to high-dose methotrexate and rituximab in newly diagnosed PCNSL patients has demonstrated promising outcomes and favorable safety profiles, advocating for the use of this combination therapy as a potential frontline treatment option for PCNSL.