Background: Diabetic ketoacidosis (DKA) is an acute life-threatening complication of diabetes. It is not only a sign of acute absolute insulin deficiency in type 1 diabetes mellitus (T1DM) but also increasingly seen in patients with type 2 diabetes mellitus. DKA can affect the function of the hypothalamus-pituitary- thyroid axis directly or indirectly due to various factors such as relatively insufficient insulin secretion and metabolic disorders. Subjects and Methods: This study was performed in the ICU of Minia University Hospital and Beni-Suef University Hospital. It included 90 patients admitted in ICU of both Hospitals who had diabetic ketoacidosis and 30 normal individuals as control group. The thyroid function of patients group and control group, impact of Ketoacidosis on thyroid function of patients group and its correlation with the clinical features and laboratory findings at diagnosis were evaluated. Results: Asregard thyroid profile TSH, FT3 and FT4 were significantly lower in patients compared to control groups (p <0.001). The mean reverse T3 was 780.1±55.6 in DKA patients, which was significantly higher than control group (325±62.5) with p value p < 0.001. The mean TSH was (1.9±0.4) in DKA patients, which was significantly lower than control group (2.6±0.6) with p value p < 0.001. The mean FT3 was (3±0.4) in DKA patients, which was significantly lower than control group (3±0.4) with p value p < 0.001. The mean FT4 was (12.9±1.3) in DKA patients, which was significantly lower than control group (13.8±1.4) with p value p < 0.013. There was significant negative association between rT3 and pH (r= -0.610, p < 0.001). Conclusions:Our study demonstrated that thyroid profile TSH, FT3 and FT4 were significantly lower in patients with DKA, while the mean reverse T3 was significantly higher in DKA patients. This dysfunction was correlated with severity of ketoacidosis. Findings of our study may have important therapeutic applications.