N-terminal pro-B-type natriuretic peptide (NT-proBNP) is suggested to be altered in patients with systolic heart failure or acute coronary syndrome. We explored the relationship between left ventricular ejection fraction (LVEF) and levels of NT-proBNP in patients with unstable angina and type 2 diabetes mellitus and preserved LVEF.Patients with unstable angina were divided into normal glucose tolerance (controls) and type 2 diabetes mellitus groups. The plasma NT-proBNP concentration was measured in these patients within 30 minute of admission for a comparative study. The severity of coronary arterial lesions was evaluated using Syntax scores. Results: NT-proBNP levels were not significantly different in patients with unstable angina and type 2 diabetes mellitus (median [quartiles]: 167.0 [66.1, 623.3] pg/mL) from those of controls (116.0 [69.8, 233.0], P = 0.278). Subsequent analyses indicated that ln (NT-proBNP) was positively associated with the following parameters: left ventricular end-diastolic diameter (r = 0.495, P = 0.019), left ventricular end-systolic diameter (r = 0.648, P = 0.001), and Syntax score (r = 0.567, P = 0.006); ln (NT-proBNP) was negatively associated with LVEF (r = -0.652, P = 0.001) in patients with unstable angina and type 2 diabetes mellitus. In multiple linear regression analysis, ln (NT-proBNP) levels were significantly independently correlated with the LVEF and Syntax score. However, no correlation was observed between ln (NT-proBNP) and each parameter in patients with unstable angina and normal glucose tolerance (controls).The NT-proBNP level is independently correlated with the LVEF in patients with unstable angina and type 2 diabetes mellitus and preserved LVEF.