Heart failure with preserved ejection fraction is recently highlighted as a major health problem, and diastolic dysfunction associated with hypertension has a dominant role in the development of heart failure with preserved ejection fraction. Osteopontin (OPN) is a secreted phosphoprotein, which mediates fibrosis. In animal models, OPN is upregulated in response to pressure overload and is thought to be involved in systolic dysfunction. However, the functional role of OPN in diastolic dysfunction is unknown. The guanine base insertion polymorphism at À156 position of the OPN promoter is postulated to upregulate the transcription of OPN in human. To investigate whether À156del/G polymorphism of OPN promoter is associated with diastolic dysfunction in hypertensive hearts, the patients with hypertension have been genotyped for variants of À156del/G polymorphism by genomic sequencing. Diastolic function of the left ventricle was estimated as the ratio of early to atrial filling (E/A ratio), obtained by pulsed-Doppler derived transmitral flow in echocardiographic analysis. The patients with À156G allele displayed lower E/A ratio compared with those with À156del/del genotype, suggesting exacerbated diastolic function. Notably, in case of the population with diabetes mellitus, the patients with À156G allele showed significant association with lower E/A ratio, compared with À156del/À156del patients. Multiple linear regression analysis revealed that prevalence of À156G allele was an independent factor for lowering E/A ratio. The À156del/G genetic variants of OPN promoter were associated with decreased E/A ratio in hypertensive patients. These results suggest that OPN has a functional role in the development of diastolic dysfunction in hypertensive hearts.