Grooved thrust air bearings are widely used to support high-speed, low-loaded shafts in many rotating systems because of their low friction, noiseless operation, and simple structure. Several types of groove geometries, such as straight line, spiral, and herringbone, are commonly used in actual applications. Among these, the spiral groove is mainly used. However, as far as the authors know, there is no theoretical evidence that the spiral groove is the most optimized groove geometry in all possible groove geometries. This paper describes the optimum design for the groove geometry of thrust air bearings according to various objective functions such as air film thickness, bearing torque, dynamic stiffness of air film, and other similar combinations. In an optimum design, groove geometries are expressed by the third degree of spline function, and sequential quadratic programming is used as the optimization method. It is understood that the groove geometry for optimizing air film thickness or friction torque takes the basic form of spiral groove geometry. The geometry design for optimizing the dynamic stiffness is the modified spiral groove. Numerical results are compared with the measured data, and good agreements can be seen between them.