The spools in most all the hydraulic spool type control valve have several circumferential grooves to prevent well known hydraulic locking problems which result in high friction force and excessive wear. In this paper, a commercial computational fluid dynamics (CFD) code, FLUENT is used to investigate the effects of groove sectional shapes and its sizes on the flow and lubrication characteristics of single grooved hydraulic spool valve. The streamlines, velocity and pressure distributions in the groove, and leakage flow through the clearance are obtained for various groove depths and sectional shapes. For shallow groove, the streamlines and leakages are highly affected by groove shapes and depths. However, for relatively deep groove, the pressure distribution and leakage are nearly uninfluenced by groove depth. It is newly found that there occurred vortices inside groove beyond a certain ratio of groove depth to width. The vortex can play as contaminants collector so contribute to reduce abrasive wear. The numerical method adopted in this paper and results can be used in optimum design of spool valves.