Objective Today we can use few medications with efficacy and safety in type 2 diabetic patients (T2DM) with renal dysfunction, though they account for almost half of Japanese T2DM. Alogliptin is a selective inhibitor of dipeptidyl peptidase 4 (DPP-4) titrated with renal function level. In order to evaluate the efficacy and safety of alogliptin based on renal function in T2DM, we designed prospective observational study (eGFR study). Methods To evaluate efficacy of alogliptin based on renal function in T2DM, we have evaluated the dosage of alogliptin, the glycemic control, eGFR and body weight in T2DM registered with this study from August 2011 to April 2013. Results Study participants were all Japanese and 487 male and 279 female. Mean age was 64 ± 12.2 years, HbA1c was 7.7 ± 1.2%, fasting plasma glucose was 144.6 ± 37.3 mg/dL, eGFR was 74.4 ± 22.6 mL/min./1.73m², body weight was 64.5 ± 13.6 kg, the dosage of alogliptin was 22.2 ± 5.7 mg. After 52 weeks follow up HbA1c was 7.1 ± 1.0% (P < 0.01), fasting plasma glucose was 129.9 ± 29.1 mg/dL (ns), eGFR was 69.2 ± 21.0 mL/min./1.73m² (P < 0.01), and body weight was 63.7 ± 12.9 kg (ns). Between two groups keeping good glycemic control for 52 weeks or not, we found the association with body weight gaining. Conclusion Treatment with alogliptin in Japanese T2DM is effective at least in 52 weeks follow up. We need to accumulate more cases, especially with moderate and severe renal dysfunction, and keep following up for more years, in order to evaluate the long-term efficacy of alogliptin based on renal function in T2DM.