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BACKGROUND: Gui Shao Tea (GST), a long-aged tea with a Chinese herbal aroma, can treat many stubborn and malignant diseases, according to traditional Chinese medicine. This research aimed to discover and define GST, study the anti-gastric cancer effects of GST extracts and preliminarily elucidate the mechanism of action in the PI3K/Akt signaling pathway and the gut microbiota. METHODS: GST was analyzed by GC/MS and HPLC. Cell proliferation, the cell cycle and apoptosis were evaluated by a CCK8 assay and flow cytometry. The effects of GST extracts on tumor inhibition and survival time were explored by a gastric cancer xenograft model in nude mice. The PI3K/Akt signaling pathway was assessed by western blotting and immunohistochemistry. Gut microbiota detection and fecal microbiota transplantation were performed to examine whether the tumor inhibition observed in mice was related to gut microbiota changes. RESULTS: The ingredients in GST, mostly terpenes and their derivatives, were novel and more concentrated than those in tea made from the branches and leaves of the same plant species, Camellia sinensis, picked and produced the same year, while the levels of polyphenols and alkaloids were significantly reduced. In BGC-823, MGC-803, and SGC-7901 gastric cancer cells, GST extracts significantly inhibited proliferation (p = 0.037), induced G0/G1 arrest (p < 0.001) and promoted early apoptosis (p = 0.041). In mice, gastric tumor growth was significantly inhibited in both the high-dose (HTF) and middle-dose (MTF) GST-fed groups. The inhibition rate in the HTF group was 33.77% on Day 14 (p = 0.042), and that in the MTF group was 55.21% on Day 14 (p = 0.002) and 61.6% on Day 28 (p = 0.008). The survival time of MTF group mice was significantly prolonged by 22.2% (p = 0.013). GST extracts inhibited the PI3K/AKT signaling pathway in gastric cancer cells (p = 0.016) and tissues (p = 0.029), downregulated the protein p-Rb and further downregulated E2F1, thereby affecting the ce