SGLT2 inhibitors have been associated with increased serum ketone bodies in patients with type 2 diabetes mellitus (T2DM). This analysis evaluated serum ketone body levels and variability in 1,278 Japanese patients with T2DM treated with canagliflozin 100 or 200 mg. Similar mean increases in ketone body concentrations of ~2-fold were seen with both canagliflozin doses. Median (interquartile range) percent change from baseline was 62% (0;180) for acetoacetate and 78% (2;236) for β-hydroxybutyrate. Approximately 2/3 of the variability in each ketone measure was attributed to intra-subject variability. Intra-subject variability was higher for serum ketones than other metabolites. Subjects in the lowest-response tertile exhibited no increase in ketones. Those in the highest-response tertile tended to be male and have higher fasting glucose, lower insulin, and longer T2DM duration at baseline. Moreover, changes in serum ketones were not fully explained by changes in plasma fatty acids, suggesting downstream effects of SGLT2 inhibition on hepatic metabolism that favour ketogenesis. In summary, increases in serum ketone bodies with canagliflozin were greater and more variable than changes in other metabolic measures in Japanese subjects with T2DM.