Abstract: 【Abstract】 Objective To determine the diagnostic value of serum beta-hydroxybutyrate (βOHB) in diabetic ketosis or diabetic ketoacidosis. Methods We conducted a retrospective review of clinical data, in West China Hospital from May 2011 to May 2013, of 1 209 patients with non-ketosis diabetics (DM group), 262 patients with diabetic ketosis or diabetic ketoacidosis (DK/DKA group), and 480 healthy people undergoing routine medical examinations (normal control group). Logistic regression analyses and ROC curves were performed in determining the diagnostic value of βOHB for DK/DKA. Results The level of serum βOHB was much higher in the DK/DKA patients than that of the participants in the DM group and normal control group (P<0.01). The serum βOHB turned negative earlier than urine ketone (P<0.01) in the DK/DKA patients. The logistic regression analysis indicated that βOHB was one of the independent risk factors for DK/DKA. The βOHB had an area under of 0.975 in ROC curve, with 1 mmol/L 〔sensitivity (Sen.) 85.1%, specificity (Spe.) 95.3%, positive predictive value (PV+) 80.36%, negative predictive value (PV-) 96.89%〕 as a diagnostic point for DK/DKA and 0.66 mmol/L (Sen. 95%, Spe.89.2%, PV+ 66.41%, PV- 99.9%) as a screening point. Conclusion Diabetic patients with a level or higher than 1 mmol/L serum βOHB can accurately predict DK/DKA. Patients with a level or lower than 0.66 mmol/L serum βOHB are unlikely to have DK/DKA.