This study aims to find the concentration of pandanus (Pandanus amaryllifolius) leaves extract that can inhibit the growth of Aeromonas hydrophllia (in vitro test) and LC50-24 hour pandan leaves extract against sangkuriang catfish fry (in vivo test). The research method used was experimental with a completely randomized design (CRD), using five treatments and three replications for the in vitro test, while for the in vivo test six treatments and two replications. The treatment for the in vitro test was pandanus leaves extract with a concentration of A. 600 ppm, B 800 ppm, C 1000 ppm and D 1200 ppm. While the treatment for the in vivo test was A. 0 ppm, B. 10 ppm, C. 100 ppm, D. 500 ppm, E.1000 ppm and F. 3000 ppm. A. hydrophilla bacteria used with a density of 108 CFU / mL Sangkuriang catfish used for the in vivo test measuring 5-7 cm. The parameters observed were the diameter of the inhibition zone and fish mortality (LC50-24 hours). Inhibition zone data were analyzed using the F test, and the 24-hour LC50 test dat1. a were analyzed descriptively. The results showed that pandanus leaves extract at a concentration of 1200 ppm was able to inhibit the growth of A. hydrophila bacteria in the strong category with an average inhibition zone diameter of 14.30 mm and an LC50-24 hour value obtained at a concentration of 1737.714 ppm. The conclusion of this study is that pandanus leaves extract can be used to treat catfish that are attacked by A. hydrophila with a concentration below 1737,714 ppm.