Boron neutron capture therapy (BNCT) is a promising therapy for refractory cancer based on the cytotoxic reaction of ¹⁰B (n, α) ⁷Li. Although two BNCT agents are clinically available, they are quickly metabolized and show modest enrichment in tumor sites, partially limiting BNCT widespread application. Consequently, novel agents that perform active targeting and show good biocompatibility have to be developed. Herein, boronophenylalanine‐containing polydopamine (B‐PDA) nanoparticles are easily fabricated by encapsulating boronophenylalanine (BPA) in polydopamine via nitrogen‐boronate coordination. In this study, B‐PDA achieves increased tumor accumulation and prolonged retention effects in the tumor site and superior antitumor activity post neutron irradiation in the orthotopic xenograft glioma model. In brief, this study offers a novel strategy for BPA delivery and may broaden the perspective on nanomedicine design for BNCT.