To evaluate the efficacy and safety of BL-B01D1, a potential first-in-class epidermal growth factor receptor (EGFR)-human EGFR 3 bispecific antibody-drug conjugated (ADC) with Ed-04, in patients with locally advanced or metastatic urothelial carcinoma (la/mUC) refractory to standard or regular therapies.BL-B01D1-201 is a multicenter, single-arm, phase II study of BL-B01D1 in patients with la/mUC who have progressed on systemic therapy. Patients received BL-B01D1 at a dose of 2.2, 2.5, or 2.75 mg/kg intravenously over approximately 60 minutes on days 1 and 8 once every 3 weeks. The primary end point was objective response rate (ORR). Secondary end points included progression-free survival (PFS), disease control rate (DCR), duration of response (DOR), and safety.A total of 41 patients were enrolled, 34 in 2.2 mg/kg, four in 2.5 mg/kg, and three in the 2.75 mg/kg group. In the 2.2 mg/kg group, the confirmed ORR was 44.1% (95% CI, 27.2 to 62.1) and the DCR was 88.2% (95% CI, 72.5 to 96.7). Among 15 patients who had received only one previous line of chemotherapy (either platinum-based or ADCs), the confirmed ORR achieved 80% (95% CI, 51.9 to 95.7). With a median follow-up of 10.2 months, the median PFS was 7.3 months (95% CI, 5.5 to 9.8) and the median DOR was 11.3 months (95% CI, 4.3 to not reached). The most common treatment-related adverse events (all grade/≥grade 3) were anemia (88.2%/38.2%), leukopenia (76.5%/38.2%), neutropenia (64.7%/41.2%), thrombocytopenia (64.7%/32.4%), appetite decrease (52.9%/2.9%), and nausea (52.9%/2.9%).BL-B01D1 showed promising preliminary efficacy and a favorable safety profile at 2.2 mg/kg in patients with la/mUC who had progressed after systemic therapy. These results suggest that BL-B01D1 could be a promising new agent for patients with la/mUC with few treatment options.