This paper presents a real-time straightness measurement and compensation system with an optical straightness measurement system and a single-axis flexure-hinge type lead zirconate titanate (PZT)-based compensation stage. The optical straightness measurement system consists of a He-Ne laser, a quadrant photodiode detector, and five right-angle reflectors. Multiple laser beam reflections between the right-angle reflectors increase the sensitivity of the straightness measurement by a factor of 6. The right-angle reflectors can be moved by the flexure-hinge type PZT-based compensation stage that is actuated by a PZT actuator to ensure that the laser beam is always projected onto the center of the quadrant detector. These two systems are integrated and fixed on a scanning stage. The resolution of the straightness measurement system is 0.1 microm. Using the real-time straightness compensation system, the straightness error of the scanning stage is fed back to the control system. The compensated straightness error of the scanning stage system was reduced from 6.5 microm to less than 1 microm.