Prostate cancer (PCa) is the most common malignancy of the male genitourinary system and currently lacks effective treatment. Semen Impatientis, the dried ripe seed of Impatiens balsamina L., is described by the Chinese Pharmacopoeia as a traditional Chinese medicine (TCM) and is used in clinical practice to treat tumors, abdominal masses, etc. In our previous study, the ethyl acetate extracts of Semen Impatientis (EAESI) was demonstrated to be the most effective extract against PCa among various extracts. However, the biological effects of EAESI against PCa in vivo and the specific antitumor mechanisms involved remain unknown.In this study, we aimed to investigate the antitumor effect of EAESI on PCa in vitro and in vivo by performing network pharmacology analysis, transcriptomic analysis, and experiments to explore and verify the underlying mechanisms involved.The antitumor effect of EAESI on PCa in vitro and in vivo was investigated via CCK-8, EdU, flow cytometry, and wound healing assays and xenograft tumor models. Network pharmacology analysis and transcriptomic analysis were employed to explore the underlying mechanism of EAESI against PCa. Activating transcription factor 3 (ATF3) and androgen receptor (AR) were confirmed to be the targets of EAESI against PCa by RT‒qPCR, western blotting, and rescue assays. In addition, the interaction between ATF3 and AR was assessed by coimmunoprecipitation, immunofluorescence, and nuclear-cytoplasmic separation assays.EAESI decreased cell viability, inhibited cell proliferation and migration, and induced apoptosis in AR+ and AR- PCa cells. Moreover, EAESI suppressed the growth of xenograft tumors in vivo. Network pharmacology analysis revealed that the hub targets of EAESI against PCa included AR, AKT1, TP53, and CCND1. Transcriptomic analysis indicated that activating transcription factor 3 (ATF3) was the most likely critical target of EAESI. EAESI downregulated AR expression and decreased the transcriptional activity of AR through ATF3 in AR+ PCa cells; and EAESI promoted the expression of ATF3 and exerted its antitumor effect via ATF3 in AR+ and AR- PCa cells.EAESI exerts good antitumor effects on PCa both in vitro and in vivo, and ATF3 and AR are the critical targets through which EAESI exerts antitumor effects on AR+ and AR- PCa cells.Copyright © 2024 The Authors. Published by Elsevier B.V. All rights reserved.