Abstract： Objective:To explore the effect and action mechanism of temozolomide combined with hyperbaric oxygen (HBO) on regulating the malignant biological behavior of glioma U87 cells via PI3K pathway.Methods:After being cultured, the U87 cells were divided into control group, temozolomide group, temozolomide + HBO group, and HBO group, according to the random number table. The cell proliferation capacity and apoptosis rate were detected by MTT assay and flow cytometry respectively. The effect of temozolomide combined with HBO on tumorigenicity of the U87 cells was analyzed in vivo by subcutaneous tumorigenesis experiments in nude mice. The levels of hypoxia inducible factor (HIF) -1α mRNA and PI3K/AKT pathway-related protens were detected by Quantitative Polymerase Chain Reaction (qPCR) and Western blotting.Results:Compared with the control group, in the temozolomide group and the HBO group, the proliferation abilities of the U87 cells decreased, their apoptosis rate increased, and the levels of HIF-1α and PI3K/AKT pathway-related protens decreased significantly ( P<0.05). The proliferation ability of the U87 cells in the temozolomide + HBO group was weaker than those in the temozolomide group and the HBO group, while its apoptosis rate was significantly higher than the rates in the two group ( P<0.05). The levels of HIF-1α and PI3K/AKT pathway-related protens of the temozolomide + HBO group were significantly lower than those of the temozolomide group and the HBO group ( P<0.05). Temozolomide could significantly inhibit glioma growth, the HIF-1α level, and the phosphorylation levels of PI3K/AKT pathway ( P<0.05). When combined with HBO, temozolomide could further inhibit glioma growth, HIF-1α expression, and PI3K/AKT pathway ( P<0.05). Conclusion:Temozolomide chemotherapy combined with HBO can suppress the proliferation of glioma U87 cells and promote apoptosis, therefore, improve the sensitivity of tumor cells; and these might be achieved by inhibiting PI3K pathway and the expression of HIF-1α.