Objective: To investigate the correlation between the expression of miR-29b in serum with the prediabetes and type 2 diabetes mellitus (T2DM), and its potential as a biomarker for auxiliary diagnosis. Methods: Relevant clinical biochemical indexes were detected by biochemical analyzer. The expression level of miR-29b in the serum of 3 groups was detected by qRT-PCR. The correlation of miR-29b and fibrinogen (FG) were analyzed in prediabetes and T2DM groups, as the same as HbA1c and oral glucose tolerance test (OGTT); Logistic regression was used to the correlation of serum miR-29b and pre-diabetes and T2DM; ROC curve analysis was used to assess value of serum miR-29b as the diagnosis of pre-diabetes and T2DM. Results: The expression of miR-29b in serum of T2DM group and pre-diabetic group was significantly higher than that of control group (P<0.05). Compared with pre-diabetic group, the expression of miR-29b was significantly increased in T2DM group (P<0.05). There was a positive correlation between miR-29b, FG, HbA1c and OGTT in the prediabetes and T2DM groups; serum miR-29b was an independent risk factor for prediabetes and T2DM. The area under the curve (AUC) of serum miR-29b as diagnose of prediabetes and T2DM were (AUC=0.681; 95% CI 0.587–0.776) and (AUC=0.757; 95% CI 0.673–0.841), respectively. Conclusion: The expression level of miR-29b in serum is a potential biomarker for the diagnosis of prediabetes and T2DM.