Cryogenic wind tunnels have been under active development for several years only. The main advantage of this type of tunnels is the possibility of obtaining high values of Reynolds number on relatively small test models. Moreover, it offers massive reduction of energy required in transonic and low speed testing. The basic idea of the cryogenic wind tunnel is to obtain flow at very low temperature in the order of 120 °k . This temper-ature is reached by injecting liquid nitrogen in the circuit of the tunnel. In order to reach correct simulation of flow on the tested model, the particles of liquid nitrogen must be evaporated completely on entering the test section of the cryo-genic wind tunnel. This paper presents a laser system developed to determine the size-distribution of liquid nitrogen particles carried in the airstream of a pilot cryogenic wind tunnel. The developed sys-tem could be used to determine size distribution functions of particles in aerosols, combustion and in a two-phase-flow ( liquid-gas) generally. It is actually feasible to be applied in this area of experimental investigations.