Background: Left ventricular diastolic dysfunction may be involved in the development of heart failure in diabetes mellitus. It has been demonstrated that candesartan cilexetil combined with ACE inhibitor effective in heart failure with preserved systolic dysfunction in clinical trial. Objective: To compare the effect of combination of candesartan and captopril with captopril monotreatment on cardiac diastolic function in diabetes. Methods: Male Otsuka Long-Evans Tokushima Fatty (OLETF) rats (n = 24), a model of spontaneously developing diabetes mellitus and diabetes resistant LETO rats (n=8) were used. At 32 weeks of age, at that time hyperglycaemia with hyperinsulinaemia was proven. OLETF were devided into combination group and monotherapy group. In combination group, candesartan was delivered 0.2 mg/kg/day with vehiecle(osmotic pump) and 50mg/Kg/d of captopril was delivered drinking water for six weeks. In monotherapy group, 100mg/Kg/day captopril was given with water. Hemodynamic parameters for diastolic function negative dP / dt and left ventricular end-diastolic pressure(LVEDP) were measured with impedance pressure volume catheter. Results: Compared with the control rats, the OLETF rats at 32 weeks showed decreased peak -dP/dt compared with LETO rats (853짹47 vs 1230짹56 mmHg/s, p<0.05) and increased LVEDP (24.3짹2.6 vs 18.9짹2.6mmHg, p < 0.05). Conclusions: Angiotensin II receptor blockade combined with ACE inhibitor probably beneficial in diastolic function in type II diabetes model.