An optical fiber droplet sizer which is applicable to droplet size measurements in a steam turbine has been developed. This sizer uses the forward scattering method. The performance of the droplet sizer was verified by 0.1–5.7 μm average diameter polystyrene particles. Using this sizer, droplet size measurements were made at the last stage moving blade outlet in a 10 MW experimental steam turbine. Average diameters between 0.2 and 1.0 μm, which depend on wetness (6–14 percent) and locations in the radial direction of the blade, were obtained.