Micro device for separating blood plasma from whole human blood and method for making the same. The micro device (1) comprises a polymer material microchip (2) having an open micro channel pattern (3) and glass plate (4) bonded against the open side of the micro channel pattern. The micro channel pattern comprise a blood flow channel (5) connected to a corpuscles flow channel (9) and a sine shaped plasma flow channel (13) through a curved constriction channel (17). The diameters of the blood flow channels are 200-400µm,80-150µm,300-600µm,and 100-150µm, respectively. The constriction channel extends through an angular distance of 90-270. The micro device is efficient, user friendly, economical and reliable