Ejector performance characteristics and design analysis of jet refrigeration systems were studied. It was shown that choking phenomena in the secondary vapor play a very important role in ejector performance. Ejector choking, which is usually associated with a hypothesized effective area for the secondary vapor in the mixing zone, takes place when the ejector is operating at a back pressure below the critical value. The effective areas analyzed from the experiment were shown not to be constant but to vary with operating conditions. A performance map was constructed from the experimental results to show the ejector performance characteristics and from which the design analysis of jet refrigeration systems was carried out. Several important features of jet refrigeration system design are summarized in the present paper. Further analyses were also made to show the performance characteristics of jet refrigeration systems operating at off-design conditions.