Background: Recently, the incidence of diabetes has increased. A rapid method for the diagnosis of prediabetes is needed. Although granulin levels are associated with obesity and insulin resistance, it remains unclear whether serum granulin concentration may serve as a biomarker of prediabetes and diabetes. Here, we examined the association between serum granulin and glycemic status in a clinical population. Methods: In total, 180 age- and sex-matched participants with normal glucose tolerance (NGT), impaired fasting glucose (IFG), impaired glucose tolerance (IGT) and newly diagnosed diabetes (NDD) were recruited. Serum granulin levels were measured via an enzyme-linked immunosorbent assay. Multivariate linear regression analysis was performed to evaluate the relationships between the level of granulin and different glycemic statuses. The utility of the granulin concentration for diagnosis of prediabetes and diabetes was evaluated with a receiver operating characteristic (ROC) curve. Results: Serum granulin concentrations were significantly greater in the IFG, IGT and NDD groups than in the NGT group. Multiple linear regression analysis revealed that obesity and glycemic status were independently associated with granulin concentrations. The ROC curve analysis revealed an area under the curve of 0.781 (95% CI, 0.709–0.853; p < 0.001). Conclusions: An elevated serum granulin concentration has potential utility as a biomarker for screening prediabetes and diabetes.