AIM: To determine the inhibitory effect of Astragalus memebranaceushas on gastric cancer cell supernatantinduced apoptosis of human peritoneal mesothelial cells. METHODS: Human peritoneal mesothelial cell (HPMC) line HMrSV5 was co-incubated with gastric cancer cell supernatant (MKN45) and/or Astragalus memebranaceushas. Morphological changes in gastric cancer cells were observed under phase-contrast microscope. Quantitative cell damage was determined by MTT assay. Apoptosis was determined under transmission electron microscope and quantified by detecting acridine orange/ethidium bromide-stained (AO/EB) condensed nuclei under fluorescent microscope or by flow cytometry. Expressions of Bcl-2 and Bax were evaluated with immunostaining. RESULTS: Morphological changes and exfoliation occurred and naked areas appeared in cultured HMrSV5 cells 24 h after they were treated with gastric cancer cell supernatant. Cell supernatant from MKN45 gastric cancer cells induced apoptosis of HMrSV5 cells in a time-dependent manner. Obvious morphological changes were observed in cell apoptosis, such as condensation of chromatin, nuclear fragmentations and apoptotic bodies. Astragalus memebranaceus could partly suppress these changes and regulate the expressions of Bcl-2 and Bax in HMrSV5 cells.CONCLUSION: Gastric cancer cells induce apoptosis of HPMCs through the supernatant. Astragalus memebranaceushas inhibits this phenomenon and can be used an adjuvant chemothera-peutic agent in gastric cancer therapy. METHODS: Human peritoneal mesothelial cell (HPMC) line HMrSV5 was co-incubated with gastric cancer cell supernatant (MKN45) and / or Astragalus memebranaceushas . Quantitative cell damage was determined by MTT assay. Apoptosis was determined under transmission electron microscope and marked by detecting acridine orange / ethidium bromide-stained (AO / EB) condensed nuclei under Expressions of Bcl-2 and Bax were evaluated with immunostaining. RESULTS: Morphological changes and exfoliation occurred and naked areas appeared in cultured HMrSV5 cells 24 h after they were treated with gastric cancer cell supernatant. Cell supernatant from MKN45 gastric cancer cells induced apoptosis of HMrSV5 cells i Obvious morphological changes were observed in cell apoptosis, such as condensation of chromatin, nuclear fragments and apoptotic bodies. Astragalus memebranaceus could partly suppress these changes and regulate the expressions of Bcl-2 and Bax in HMrSV5 cells. CONCLUSION: Gastric cancer cells induce apoptosis of HPMCs through the supernatant. Astragalus memebranaceushas inhibits this phenomenon and can be used an adjuvant chemothera-peutic agent in gastric cancer therapy.