Objective: Ketone body has been paid attention for several metabolic benefits recently. However, clinical meaning of elevated ketone levels in type 2 diabetes (T2DM) has not been concluded. This study aimed to investigate clinical implication of baseline ketone levels in patients with newly diagnosed T2DM who visit outpatient clinic. Methods: We enrolled 81 subjects from outpatient clinic who evaluated serum beta-hydroxybutyrate (BHB) at the time of diagnosis of T2DM. A higher serum BHB level was defined as the highest tertile of BHB (≥ 0.3 mmol/L). The associations of the baseline BHB levels with glucometabolic indices at baseline, and 3 and 6 months after treatment were analyzed. Results: Patients with elevated BHB levels revealed significantly higher HbA1c and glucose levels in association with decreased insulin secretory markers. Initial BHB levels were markedly correlated with hyperglycemia and decreased insulin secretion, but not correlated with insulin resistance. On the other hand, after adjusting for confounding factors, a baseline BHB level itself was an independent predictive marker for a greater HbA1c reduction after 6 months, even in the analyses constricted to insulin users only. Furthermore, subjects in the highest tertile of BHB levels were more likely to obtain glycemic control (HbA1c < 6.5%) after 6 months of antidiabetic management. Conclusion: In newly diagnosed patient with type 2 diabetes, baseline BHB levels were significantly associated with decreased insulin secretion and more severe hyperglycemia. However, a baseline BHB level was a significant predictive marker for future HbA1c reduction and, surprisingly, this trend was consistent even among insulin users only. Our data suggest a potential clinical benefit of ketone body in patients with newly diagnosed type 2 diabetes.