Aims. Heterozygous mutations of the hepatocyte nuclear factor (HNF)-4α gene cause a particular form of maturity-onset diabetes of the young (MODY1). Recent genetic studies have shown that single nucleotide polymorphisms (SNPs) of the β-cell type P2 promoter of the HNF-4α gene are associated with type 2 diabetes in some populations. In the Japanese population, a haplotype consisting of two SNPs (rs1884614 and rs2144908) in the P2 promoter region is reported to show a significant association with type 2 diabetes. Methods. Both rs1884614 and rs2144908 were genotyped in 349 type 2 diabetic patients and 203 non-diabetic controls. The relation of these SNPs to clinical characteristics was also examined in the diabetic subjects. Results. There were no differences in the genotype distribution of the two SNPs between the control and diabetic subjects, and the haplotype distribution was also similar in the two groups. However, the rs1884614 T/T genotype was significantly associated with a smaller area under the plasma insulin curve (AUC) during the OGTT in non-obese (BMI <25 kg/m ² ) patients (p = 0.0272; adjusted for age and sex). Conclusions. SNP rs1884614 in the P2 promoter region of the HNF-4α gene may influence insulin secretion in non-obese Japanese subjects with type 2 diabetes.