This paper presents an ultrasonic mist generator used as an evaporative pre-cooler for air-cooled condensers in air conditioning applications. Ultrasonic mist generators eliminate pressure loss at the inlet air stream to the condenser and allow controlling the characteristics of the water atomized droplets. A water mist generation unit has been designed, built, and tested to assess its thermal performance and its water mist production capacity in terms of the mass flow rate of atomized water and size distribution of the droplets generated. To evaluate the performance and cooling capacity of the water mist produced by the ultrasonic mist generator, a set of tests has been conducted on a test bench consisting mainly of a subsonic wind tunnel equipped with instrumentation and control devices to modify the operating conditions. A Sauter mean diameter D 3, 2= 13. 2 μ m has been determined using a photographic technique for the size distribution of the generated droplets and the range of water mist flow rates that the system can produce is between 0. 11× 1 0− 3 and 0. 52× 1 0− 3 kg∕ s. It has been found that, under many operating conditions, the evaporative cooling process is not homogeneous throughout the air flow, so a novel performance indicator called ε LCP (local cooling performance) has been defined to specifically evaluate this phenomenon. A maximum direct evaporative cooling efficiency ε DEC= 83. 7% is obtained for a water-to-air ratio r w= 0. 35× 1 0− 3 and air flow rate 630 m 3/h. The maximum values of average evaporative cooling efficiency ε AEC= 65% and average temperature decrease T drop= 4.3° C are obtained for r w= 2. 41× 1 0− 3 and air flow rate 630 m 3/h.