This paper presents an optical probe employed for edge contour measurement of single point diamond cutting tools. A laser beam from a laser diode (LD) is focused by an objective lens to form a small light spot with a radius of approximately 20 μm, and is then received by a photodiode (PD) after passed through a focal point of the objective lens. A cutting edge of the tool, which is placed on a line with the LD and the PD, is inserted into the laser beam section. At an each X-position, the output of the PD is recorded while the light spot is moved along the Z-direction, scanning across the cutting edge of the tool with its rake face aligned in the XZ plane. The Z-position of the cutting edge is evaluated by determining a specific value from the obtained outputs of the PD. The edge contour of the diamond cutting tool can thus be measured by repeating the Z-scanning at different X-positions. Computer simulation was carried out to investigate the influences of error factors on the evaluation of the cutting edge. Experiments were also carried out to measure a round nose of the tool with a nominal nose radius of 2 mm.