The effects of laser irradiation on erythrocyte deformability and related mechanism were investigated. Membrane attached hemoglobin (Hbm) is the determinant factor of erythrocyte deformability. After irradiation of 532 nm (30 mW, 20 minutes) or 632.8 nm (30 mW, 60 minutes), the content of Hbm lowered and the deformability of erythrocytes increased, indicating that the decreasing of Hbm is one of the mechanisms of laser action to improve the erythrocyte deformability. The 532-nm laser is more efficient than 632.8 nm laser in the action, which is consistent with the absorption spectrum of Hbm, confirming that the Hbm is the target molecule under laser irradiation.