The aim of this poster is to determine the droplet size distribution in low water clouds from measured optical parameters. Those measurements are obtained by a Lidar system. It consists of two reception telescopes: the first is near the beam send to the atmosphere, the second is at 7.7 m-distance from the first. The backscattering signal collected by the first telescope gives after an Klett's inversion, the volume extinction coefficient profile in the cloud. The double- scattering signal collected by the second telescope associated with the volumique extinction coefficient profile, gives by an inversion method, the double-scattering phase function which is correlated to a log-normal size distribution. The collected signals are detected simultaneously. A verification of the water phase is made by the depolarization ratio. Because of the situation of Lannion city, near the sea, swept by predominant winds from West, frequent fronts are present. So, a large diversity of clouds exists, which is a good experimental ground for testing and validating the theory presented here. Results from ENSSAT Lidar measurements will be presented.