Aims: This preliminary randomized, parallel-group comparative study evaluated the efficacy of ipragliflozin for reduction of small dense low-density lipoprotein cholesterol (sd LDL-C) levels in Japanese patients with type 2 diabetes mellitus (T2DM). Methods: Sixty-two patients with T2DM (age, 56 +/- 8 years; hemoglobin A1c levels, 8.1 +/- 0.9%; BMI, 27.5 +/- 3.3 kg/m(2)) were randomly assigned in a 2: 1 ratio to receive ipragliflozin (50 mg/day) (treatment group; n=40) or continued treatment (control group; n=22) for 12 weeks. The primary endpoints were changes in sd LDL-C levels detected using the LipoPhor AS((R)) system; the secondary endpoints included changes in the sd LDL-C/large buoyant LDL-C (lb LDL-C) ratio, a surrogate marker for LDL particle size, and percent changes in routine lipid parameters. Results: The treatment group exhibited a statistically significant reduction from baseline for LDL-C levels (-0.37 mg/dL vs. 14.4 mg/dL, p=0.038), sd LDL-C levels (-1.28 mg/dL vs. 2.81 mg/dL, p=0.012), and sd LDL-C/lb LDL-C ratio (-3.20% vs. 4.58%, p=0.040) compared with the control group. Multiple regression analysis among all subjects revealed change in TG levels (p=0.011) and LDL-C levels (p=0.024) as well as change in body weight (p=0.006) as independent factors contributing to the reduction in sd LDL-C. Conclusions: Ipragliflozin may have a potential for lowering sd LDL-C levels associated with increasing LDL particle size in Japanese patients with T2DM. (C) 2016 The Authors. Published by Elsevier Inc.