Objective To investigate the changes of serum sialic acid (SA) and C-reactive protein (CRP) in patients with obstructive sleep apnea hypopnea syndrome (OSAHS) and type 2 diabetes mellitus (T2DM).Methods A total of 105 subjects were included in the study. 30 health controls were set as health controls group, 45 OSAHS patients were set as OSAHS group, and 30 OSAHS patients complicated with type 2 diabetes were set as OSAHS patients complicated with type 2 diabetes group. All patient were inquired general information of patients. CRP, SA, FIB, and other indicators were collected through laboratory tests, and respiratory parameters was monitored by portable sleep apnea detector. All data are analyzed finally.Results The levels of CRP and SA in OSAHS group and OSAHS combined with T2DM group were higher than those in healthy control group (P < 0.05); The levels of CRP and SA in OSAHS combined with T2DM group were higher than those in OSAHS group (P < 0.05). There was significant difference in AHI, MSaO₂ and hi between OSAHS combined with T2DM group and OSAHS group and healthy control group (P < 0.05). There was significant difference in AHI, hi and MSaO₂ between OSAHS combined with T2DM group and OSAHS group (P < 0.05). BMI, SA and FBG were the risk factors of hypoventilation (P < 0.05). Logistic stepwise regression analysis showed that CRP [O^R = 1.258 (95% CI: 1.014, 1.561) ], SA [O^R = 4.232 (95% CI: 1.026, 17.460) ], and HI [O^R = 1.264 (95% CI: 1.003, 1.594) ] were independent risk factors for OSAHS patients with T2DM (P < 0.05). Correlation analysis showed that serum SA and CRP were positively correlated with AHI (P < 0.05), positively correlated with FBG (P < 0.05), and negatively correlated with MSaO₂ (P < 0.05).Conclusions There is a correlation between the level of SA and sleep disorders in OSAHS patients. High levels of SA and CRP are risk factors for type 2 diabetes in OSAHS patients, which should be paid attention to.