Background: TQB2450 is a humanized monoclonal antibody targeting programmed death-ligand 1 (PD-L1). Anlotinib is an antiangiogenic small molecule, multi-target tyrosine kinase inhibitor that has improved clinical outcomes in various solid tumors. This phase 1b study aims to evaluate the safety and efficacy of TQB2450 plus anlotinib for patients with advanced triple-negative breast cancer (TNBC) after the failure of standard therapy. Methods: This ongoing study included a dose-escalation phase and an expansion phase. Advanced TNBC patients with prior anthracyclines and/or taxanes treatment and failed at least first-line therapy were enrolled. In the dose-escalation phase, eligible patients received anlotinib (8mg, 10mg, and 12mg, qd, days 1-14; 21 days per cycle) plus TQB2450 (1200mg, day 1; 21 days per cycle) following the conventional 3+3 design. If the starting dose of 10mg anlotinib led to ≥2 dose-limiting toxicities (DLTs), 8mg anlotinib would be administered. After the dose-escalating phase, eligible patients were enrolled into the expansion cohort. The primary endpoint was objective response rate (ORR), and the secondary endpoints were overall survival (OS), disease control rate (DCR), progression-free survival (PFS), and safety. Results: Between May 29, 2019, and December 31, 2020, in the dose-escalation phase, three patients receiving 10mg anlotinib plus 1200mg TQB2450 had no DLTs in the first cycle, neither did three patients with 12mg anlotinib plus TQB2450. Next, 28 patients with advanced TNBC received 12 mg anlotinib plus TQB2450 in the expansion phase. Finally, a total of 34 patients were included with median age of 49.5 (32-70) and median prior lines of 2 (1-6). Numbers of patients with prior platinum therapy: 16, prior anthracycline therapy: 32. The ORR was 26.47% (9/34) and DCR was 82.35% (28/34). The median PFS was 8.57 months. Seventeen patients experienced grade 3 treatment-related AEs (TRAEs). Most frequently occurring (>5%) grade 3 TRAEs were QT interval prolongation (17.65%), hypertension (14.71%), diarrhea (8.82%), hand-foot syndrome (HFS) (8.82%), and hypertriglyceridemia (5.88%). Conclusions: TQB2450 plus anlotinib showed an acceptable safety profile with promising activity for previously anthracyclines and/or taxanes-treated advanced TNBC patients. Clinical trial information: NCT03855358.