Abstract： Objective:To study the effects of hyperbaric oxygen (HBO) treatment on partial pressure of oxygen (PaO 2) and malignant biological behavior of gastric cancer cell line SGC7901. Methods:After culture, the gastric cancer cell line SGC7901 was divided into HBO group and control group. The control group did not receive any treatment, while the SGC7901 in the HBO group was treated with HBO. The PaO 2 in cell culture medium was measured by blood gas analyzer. Morphological changes of SGC7901 cells before and after HBO treatment were observed by an inverted microscope. The cell apoptosis after HBO treatment was detected by Hoechst33258 staining. The expression level of HIF-1α protein in SGC7901 cells after HBO treatment was detected by Western blotting. Results:The blood gas analyzer can accurately detect the PaO 2 of cell culture medium, and the PaO 2 of cell culture medium in the HBO group was significantly higher than that in the control group ( P<0.05); moreover, the PaO 2 of cell culture medium in the HBO group decreased slowly at different time points. After HBO treatment, the morphology of SGC7901 cells became round and the intercellular connection was loose. The Hoechst33258 staining showed that, after HBO treatment, no significant cell apoptosis was observed in SGC7901 cells in the HBO group as compared with the control group ( P>0.05). Western blotting results showed that the expression level of HIF-1α in the HBO group was significantly lower than that in the control group ( P<0.05). Conclusion:HBO treatment can obviously increase the PaO 2 in the culture medium of gastric cancer cell line SGC7901, effectively relieve the hypoxia state of SGC7901 cells, and down-regulate the expression of HIF-1α protein.