OBJECTIVE The prognostic value of programmed death ligand-1 (PD-L1) expression in triple-negative breast cancer (TNBC) has not been sufficiently investigated. In this study, we examined whether PD-L1 expression status is associated with clinicopathological features and outcomes of patients with TNBC. METHODS Immunostaining for PD-L1 SP142 was performed on tissue microarrays containing 132 TNBC samples. High PD-L1 expression was defined as ≥10% of the tumor area occupied by PD-L1-expressing cells. RESULTS Thirty-five (26.5%) patients showed high PD-L1 SP142 expression on immune cells (ICs). High IC PD-L1 expression was significantly correlated with smaller tumor size (p=0.030), absence of lymphovascular invasion (p=0.024), and fewer lymph node metastases (p=0.002). Multivariate survival analysis revealed that high IC PD-L1 expression independently predicted better disease-free survival (DFS) of TNBC patients. CONCLUSIONS High PD-L1 SP142 expression on ICs was significantly associated with favorable clinicopathological parameters and better outcomes in patients with TNBC. Our observations suggest that high IC PD-L1 expression can be used as an independent prognostic marker for predicting better DFS in patients with TNBC.