The movement of a flowing cell near the oblique micro groove on the bottom surface in the micro flow channel has been measured to sort biological cells in vitro. The micro groove of the rectangular shape (4.5 μm depth, and 0.2 mm length) was fabricated on the polydimethylsiloxane (PDMS) disk by the photolithography technique. The angle between the flow direction and the longitudinal axis of the groove is 45 degree. Variation has been made on the width (0.03 mm < w < 0.05 mm) of the groove. A rectangular flow channel (0.05 mm height × 1 mm width × 25 mm length) has been constructed between two transparent PDMS disks. C2C12 (mouse myoblast cell line) was used in the test. A flow velocity (0.1 mm/s < vx < 2.4 mm/s) of the suspension of cells was controlled by the pressure difference between the inlet and the outlet. The shifted distance of each cell along the oblique groove depends on the diameter of the cell. The malnourished cell with the different density can be distinguished by the shifted distance according to the velocity of the cell.