Abstract  [Aim]  To investigate the potential of Oenopia formosana as a biological control for the Asian citrus psyllid Diaphorina citri, and determine if they prefer D. citri to Lipaphis erysimi. [Methods]  The predatory functional response, search efficiency and preference of O. formosana for the 1st, 2nd, 3rd and 4th instar nymphs, and adult stages up to the 5th instar nymph of D. citri, were studied under laboratory conditions. [Results]  All stages of O. formosana preyed on the 5th instar nymph of D. citri, and the functional response of all stages fitted the Holling Ⅱ model. The instant attack rates of O. formosana 1st to 4th instar nymphs and adults towards D. citri were 0.279, 0.430, 0.689, 0.829 and 0.695, respectively, Maximum daily predation rates were 29.155, 32.895, 46.512, 58.824 and 79.365 prey, respectively, and the predation capacity was 8.148, 14.131, 32.048, 48.747 and 55.130, respectively, and the processing times were 0.034, 0.030, 0.022, 0.017 and 0.013 d, respectively. The search effort of all stages decreased with increasing density of D. citri, showing the most obvious decline in the 4th instar. At low D. citri densities, 4th instar O. formosana had the highest search effort. When 5th instar nymphs of D. citri and adult L. erysimi were both present, adult O. formosana preferred to prey on D. citri. [Conclusion]  All life-stages of O. formosana have the potential to control 5th instar D. citri nymphs, but 4th instar and adults are more likely to be effective biological control agents for D. citri than 1st to 3rd instar nymphs.