Abstract This paper presents an investigation on the component efficiencies of a small two-phase ejector. The experiments are firstly carried out to test the operation characteristics of a small two-phase ejector working with R600a. Combining the measured experimental data with an ejector model, a calculation method for the component efficiencies of the small two-phase ejector including the motive nozzle, mixing chamber and diffuser is proposed. The results reveal that the ejector component efficiencies vary obviously with geometric parameters and operational conditions. The motive nozzle, mixing chamber and diffuser efficiencies vary from 0.513 to 0.750, 0.492 to 0.755 and 0.610 to 0.734 under the studied conditions, respectively. Moreover, three empirical correlations for the above mentioned component efficiencies are summarized. The present study is hoped to be useful for the modeling and design of the two-phase ejector and contributes to the further researches on the variable characteristics of ejector component efficiencies.