This open-label, parallel-group study evaluated the effect of mild and moderate hepatic impairment on the pharmacokinetics of a single dose of luseogliflozin in Japanese subjects. Thirteen subjects with hepatic impairment (mild, n = 8; moderate, n = 5) and 6 healthy subjects received a single 5-mg dose of luseogliflozin. Serial blood sampling over 72 hours and 24-hour urine collection were done for pharmacokinetic analysis of luseogliflozin and its metabolites and to measure pharmacokinetic and pharmacodynamic parameters, respectively. Demographic characteristics were similar at baseline for both groups. Geometric mean ratios of maximum plasma concentration (Cmax) and area under the plasma concentration–time curve from time zero to infinity (AUCinf [90%CI]) of unchanged luseogliflozin were 1.02 (0.790–1.32) and 0.774 (0.580–1.03), respectively, on comparing patients with hepatic impairment with healthy subjects, and 0.939 (0.752–1.17) and 1.00 (0.780–1.28), respectively, in subjects with mild and moderate hepatic impairment. Although mean plasma concentrations of metabolites were slightly higher in patients with hepatic impairment versus healthy subjects, their time-course plasma concentrations were very low compared with those of unchanged luseogliflozin. Single-dose luseogliflozin 5 mg was well tolerated by study participants, indicating luseogliflozin dose adjustment is not necessary in patients with mild and moderate hepatic impairment.