Objective: To discuss the expression of RUNX2 and MDM21 in rats with periodontitis under the chronic intermittent hypoxia. Methods: A total of 32 SD healthy rats were randomly divided into four groups, with 8 rats in each group. The molecular biological techniques of immunohistochemistry, RT-PCR and Western blotting were employed to detect the effect of different hypoxia time(0, 6, 12, 24 and 48 h) and different concentrations of hypoxia(0.000, 0.001, 0.010, 0.060 and 0.100 ppm) on the expression of RUNX2 and MDM21 in rats of four groups. Results: The expression of RUNX2 and MDM21 in each group was significantly higher than the one at other concentrations when the concentration was 0.010 ppm, with the statistical difference(P<0.05). The expression of RUNX2 and MDM21 was that normoxic control group > periodontitis group> chronic intermittent hypoxia group > compound group under the action with the concentration of 0.010 ppm for 12 h, but there was no significant difference for the comparison among groups(P>0.05). Conclusions: The condition of chronic intermittent hypoxia can reduce the expression of RUNX2 and MDM21 in rats with periodontitis and aggravate the damage of periodontal bone. Methods: A total of 32 SD healthy rats were divided into four groups, with 8 rats in each group. The molecular biological techniques of immunohistochemistry, RT-PCR and Western blotting were employed to detect the effect of different hypoxia time (0, 6, 12, 24 and 48 h) and different concentrations of hypoxia (0.000, 0.001, 0.010, 0.060 and 0.100 ppm) on the expression of RUNX2 Results: The expression of RUNX2 and MDM21 in each group was significantly higher than the one at other concentration when the concentration was 0.010 ppm, with the statistical difference (P <0.05) MDM21 was that normoxic control group> periodontitis group> chronic intermittent hypoxia group> compound group under the action with the concentration of 0.010 ppm for 12 h, there was no significant difference for the compa rison among groups (P> 0.05). Conclusions: The condition of chronic intermittent hypoxia can reduce the expression of RUNX2 and MDM21 in rats with periodontitis and aggravate the damage of periodontal bone.