Abstract： Objective:To explore and analyze the effect of hyperbaric oxygen（HBO）on insulin sensitivity and endothelial function in gestational diabetic mice.Methods:A total of 60 clean-class pregnant C57BL/6J mice were selected to establish gestational diabetic mouse models，and they were randomly divided into model group，positive group，and HBO group according to the digital table method，with 20 mice in each group. The model group consisted of diabetic mice，and the positive group consisted of diabetic mice with insulin resistance. The diabetic mice with insulin resistance in the HBO group was treated with HBO. The fasting insulin level was measured by the enzyme-linked immunosorbent assay（ELISA）and the homeostatic model assessment of insulin resistance（HOMA-IR）was calculated. The endothelium-dependent dilation mediated by acetylcholine（ACh）and the endothelium-independent dilation mediated by nitroglycerin（NTG）were measured by high performance liquid chromatography（HPLC）to evaluate the endothelial function of mice.Results:Compared with the model group，the positive group had significantly decreased fasting blood glucose and fasting insulin levels，and significantly increased hepatic glycogen level（ P<0.05）. Compared with the positive group，the HBO group had significantly decreased fasting blood glucose and fasting insulin levels，and significantly increased hepatic glycogen level（ P<0.05）. Compared with the model group，the positive group had higher expression of neuropeptide Y and lower HOMA-IR（ P<0.05）；compared with the positive group，the HBO group had significantly higher expression of neuropeptide Y，and significantly lower HOMA-IR（ P<0.05）. Compared with the model group，the levels of ACh and NTG in the positive group were significantly increased（ P<0.05）；while compared with the positive group，the levels of ACh and NTG in the HBO group were significantly higher（ P<0.05）. Conclusion:HBO can improve the levels of fasting blood glucose and neuropeptide Y，enhance insulin sensitivity，and improve vascular endothelial function in mice with gestational diabetes mellitus.