The knife-edge method is a commonly used technique to characterize the optical profiles of laser beams or focused optical spots. In this paper, we present the design, fabrication, and test of a micro knife-edge scanner based on the micro-electromechanical-system (MEMS) technology. Silicon-on-insulator (SOI) processes are used to demonstrate the feasibility of the new device, whereas the CMOS-MEMS processes are used to enable the integration of the photo detector and on-chip signal conditioning circuitry. Focused optical spot size measured by the reflection-type SOI device is demonstrated to be close to the diffraction limit. Preliminary measurement results of the CMOS-MEMS device are also presented.