Esophageal squamous cell carcinoma (ESCC) is a common type of human oral malignancy with poor survival. Presently, it is necessary to find new and effective drugs for clinical therapy. This study aimed to identify the potential anti-tumor effects of ACP-5862, a major metabolite of acalabrutinib, on human ESCC progression, and to reveal the underlying mechanisms. Our findings suggested that ACP-5862 treatments markedly reduced the cell proliferation of ESCC cell lines in a time- and dose-dependent manner, while had no significant cytotoxicity to normal cells. Cell cycle arrest in G2/M phase was markedly induced by ACP-5862 in ESCC cells. Furthermore, apoptosis and endoplasmic reticulum (ER) stress were detected in ESCC cells treated with ACP-5862. Intriguingly, ACP-5862-induced apoptotic cell death was partly dependent on ER stress. Moreover, reactive oxygen species (ROS) was greatly triggered in ACP-5862-incubated ESCC cells, which was closely involved in apoptosis and ER stress mediated by ACP-5862. In addition, we showed that the expression of nuclear factor-erythroid 2-related factor-2 (Nrf2) was considerably reduced in ACP-5862-treated cells. Importantly, ACP-5862 combined with Nrf-2 knockdown could further induce apoptosis and ER stress in ESCC cells compared with the ACP-5862 single group. Animal studies confirmed that repressing Nrf-2 promoted the anti-tumor effect of ACP-5862 on ESCC growth. Taken together, these findings demonstrated that ACP-5862 exerted anti-cancer effects on ESCC through inducing ER stress-mediated apoptosis via the ROS production. Meanwhile, ACP-5862 co-treated with Nrf-2 inhibitors may supply new and effective therapeutic strategies for ESCC treatment in future. (C) 2020 Published by Elsevier Inc.