This paper describes high-speed positioning of a surface motor-driven planar motion stage with a XYθz surface encoder. The surface motor consists of two pairs of linear motors. The magnetic array is mounted on the platen and the stator winding of the linear motor on the stage base. The platen can be moved in the X- and Y-directions by the X-linear motors and the Y-linear motors, respectively. It can also be rotated about the Z-axis by a moment about the Z-axis by the X- or Y-linear motors. The surface encoder consists of two two-dimensional angle sensors and an angle grid with two-dimensional sinusoidal waves on its surface. The angle grid is mounted on the platen. The sensors are placed inside the stage for a compact design of the stage system. The surface encoder is improved for high speed positioning. Measurement errors of the surface encoder using two kinds of detectors, the quadrant PD and two-dimensional PSD, are estimated by simulation. A modification of the motors for increasing the speed of the stage is also carried out. Verification experiments of the improved system are also performed.