Using the blood samples of animal, the in vitro effects of low power laser irradiation on erythrocyte rheology were investigated. After the deposited pig′s erythrocytes (the deformation of erythrocytes have already turned to worse) were irradiated with laser, the effects of laser irradiation on erythrocyte′s deformation were measured. When 650 nm laser was used for irradiation, the deformability of erythrocytes was improved obviously. The changing tendency is that, the erythrocyte′s deformation was enhanced with the increasing of irradiation power and then saturated around 4～5 mW. When the blood samples were irradiated by 650 nm and 632.8 nm lasers respectively with the same power (10 mW), the erythrocyte deformability in two cases were all obviously increased to the similar level. These phenomena can be explained by that, the hemoglobin in erythrocytes has the similar absorption to both lasers. Taking the mouse blood as the samples, the effects of laser irradiation on erthrocyte′s electrophoretic mobility was studied further. When irradiated by 632.8 nm laser, the electrophoretic mobility of erythrocytes was speeded also, reflecting the electric charges on the surface of erythrocytes were increased which will help to decrease the aggregation of erythrocytes. Under such low power irradiation (less than 20 mW), no morphological change was detected by the microscopy and no hemolysis was found also.