Objective To investigate the clinical value of bloodβ-hydroxybutyric acid and urine ketone in the diagnosis of diabetic ketosis. Methods One hundred and fifteen patients with non-ketosis diabetics (NDK group), 85 patients with diabetic ketosis (DK group) and 105 healthy people (control group) were enrolled in Chengmai People's Hospital from May 2012 to May 2014. Blood β-hydroxybutyric acid, urine ketone and blood glucose were detected; the correlation index of blood β-hydroxybutyric acid, urine ketone and blood glucose in NDK group and DK group were analyzed. The receiver operating characteristic curve (ROC) was performed in determining the diagnostic value of bloodβ-hydroxybutyric acid for diabetic ketosis. Results The level of bloodβ-hydroxybutyric acid, positive rate of bloodβ-hydroxybutyric acid, urine ketone and level of blood glucose in DK group were higher than those in NDK group and NC group (P<0.01) . Blood β-hydroxybutyric acid was positively correlated with urine ketone and blood glucose (r=0.552,P=0.000;r=0.405,P=0.010) . When urine ketone was used as diagnostic standard, the area under curve of bloodβ-hydroxybutyric acid was 0.839, the best cutoff value ofβ-hydroxybutyric acid was 0.64 mmol/L with the sensitivity was 81.6%and specificity was 89.2%. Conclusions Examinations of bloodβ-hydroxybutyric acid and urine ketone have great significance for the diagnosis of diabetic ketosis. The co-monitoring of blood β-hydroxybutyric acid and urine ketone can reduce the rates of missed diagnosis and misdiagnosis. The best cutoff value of β-hydroxybutyric acid to diagnose diabetic ketosis was 0.64 mmol/L.