The pathogenesis of diabetic microangiopathy has been considered to be closely related with abnormal viscous blood flow and hypercoagulability in microcirculation. This study aims to find good indices for forecasting the incidence of aggravation of microangiopathy in diabetes. Two kinds of devices have been applied to investigate the rheologic property in diabetics, especially the viscoelasticity in anticoagulation and clotting state of blood. OP-Rheometer system for non-clotting blood and a viscoelastorecorder (VER) for clotting process were used to observe each significance of viscoelasticity for contribution to microangiopathy respectively. The abnormality in viscoelasticity of the blood was well correlated with plasma fibrinogen and the severity of microangiopathy. In VER maximum value of dynamic rigidity modulus (G'm) was a good index for hypercoagulable state which includes high plasma viscosity, the increased plasma fibrinogen, high red cell aggregation and the severity of retinopathy. To correlate in vivo study with in vitro examination tests, we observe the intravascular erythrocyte aggregation (IEA) in bulbar conjunctiva by a biomicroscopy. There was a good correlation of IEA to G'm and other hemorheological factors. In conclusion, elevation of both viscoelasticity of blood and clotting process (G'm) and high grade IEA suggest the increase of the incidence of aggravation on diabetic microangiopathy.