A freezing technique for measuring the size of droplets was developed to obtain the droplet size distribution in a horizontal annular flow in a pipe with a 37.1 mm diameter. Droplets are frozen by using an extremely low temperature nitrogen gas with liquid film extraction. They are then photographed with a microscope and a CCD camera and measured by means of an image process. The results are compared with various experimental data. The droplet sizes measured by the freezing technique are comparable with those measured by other methods at a high air superficial velocity (of 50 m/s). However, because of the film extraction problem, the droplet sizes measured at a low air superficial velocity of less than 40 m/s are higher than those measured by other methods. A suggested method of predicting the Sauter mean diameter is based on the maximum droplet size correlation for the experimental data, with and without liquid film extraction. The average droplet size is remarkably smaller downstream of the liquid film extractor because large droplets from the liquid film are excluded. (C) 2010 Elsevier B.V. All rights reserved.