Abstract: The erythrocyte deformability mainly depends on the composition of the membrane and cytoplasm, which consist of hemoglobin and other constituents. The most of current devices to measure erythrocyte deformability require washing process after the measurement which is labor-intensive and time-consuming. This article introduces an improved measuring system based on microfluidic and machine vision (RSD) which adopts disposable microfluidic channel and conventional laser-diffraction technique to determine erythrocyte deformability. To validate the accuracy and repeatability of RSD, several experiments are conducted to determine deformability of normal erythrocytes measured by RSD and a conventional ektacytometer(LORCA). The measured Elongation Index (EI) by RSD, which is a parameter directly related to erythrocyte deformability, is in excellent agreement with it measured by LORCA.