An ultra-thin spindle motor having a groove formed on the outer circumferential surface of a thrust bearing is disclosed. The present invention relates to an ultra-thin spindle motor among small-sized motor using a hydro dynamic pressure generating bearing and its object is to provide a spindle motor capable of stably driving without requiring a sleeve that was required to support a shaft in a radial direction in which a thrust bearing sleeve for coupling a hub and a thrust bearing is constructed and a radial hydro dynamic pressure generating groove is formed on the outer circumferential surface to thereby allow a radial hydro dynamic pressure to be generated and support a thrust bearing sleeve coupled integrally to the hub. Accordingly, the ultra-thin spindle motor having a groove formed on the outer diameter of a thrust bearing which uses a hydro dynamic bearing according to the present invention has a structure doing not need a sleeve to support the shaft, and fabricates a groove on the outer circumferential surface of the thrust bearing to thereby overcome structural thickness in manufacturing the spindle motor, compared to conventional spindle motors having a structural problems that need a sleeve to support the shaft by generating a radial dynamic pressure and have a limitation in shortening the length of shaft to form a radial dynamic pressure generating groove, and can comply with the requirements for main properties required in the spindle motor for HDD such as a low non repeatable run out (low NRRO), low noise, high speed rotation, high intensity, low power consumption, high confidence, a small size, low dust, low cost and the like.