Triple negative breast carcinoma (TNBC) is a rapid progressive tumor and has a poor overall survival. Therefore, it is crucial to find out effective molecular targets and develop optimal therapeutic strategies for TNBC. In this study, immunohistochemical staining was used to detect expressions of programmed death-ligand 1 (PD-L1) and phosphatase and tensin homolog (PTEN) in 136 breast carcinomas including 50 TNBC. The effect of PTEN on regulation of PD-L1 expression was assessed in vitro in the PTEN knockdown TNBC cells. We found that PD-L1(SP142) positive rate in TNBC (48.0%) was significantly higher than non-TNBC (23.3%). PTEN negative rate was 42% in TNBC. The inverse correlation between PTEN and PD-L1(SP142) expression in TNBC was statistically significant (P<0.05). After PTEN knockdown, PD-L1 expression in TNBC cells increased significantly, and the expression level of AKT increased simultaneously. PTEN knockdown promoted cell proliferation, viability and G1/S switch of TNBC cells. These results suggested that PTEN may involve in regulation of PD-L1 expression, because PTEN loss can upregulate PD-L1 expression in TNBC. Antitumor immunity of PD-L1 could be enhanced in TNBC when targeting PTEN at the same time.