ABSTRAK Penelitian ini bertujuan untuk mengetahui efektivitas antibakteri ekstrak daun ketepeng cina (C. alata L.) dalam menyembuhkan ikan nila (O. niloticus) yang diinfeksikan A. hydrophila dengan dosis 108 CFU/ml. Penelitian ini dilakukan di Laboratorium Balai Budidaya Perikanan Air Payau (BBPAP) Ujung Batee, Kabupaten Aceh Besar dan Laboratorium FKIP Kimia Unsyiah pada bulan September hingga Desember 2014. Penelitian ini menggunakan metode Rancangan Acak Lengkap dengan tiga taraf perlakuan konsentrasi ekstrak dan tiga perlakuan lama rendaman serta dua kontrol. Perlakuan konsentrasi ekstrak meliputi 10, 15, dan 20% dengan lama rendaman 2, 4, dan 6 menit serta kontrol negatif (ikan uji hanya disuntikan dengan larutan PBS) dan kontrol positif (ikan uji hanya diinfeksikan A. hydrophila tanpa diberi perlakuan ekstrak). Hasil uji ANOVA menunjukkan bahwa ekstrak daun ketepeng cina berpengaruh nyata terhadap kelangsungan hidup ikan nila yang diinfeksikan A. hydrophila pada taraf uji 5%. Uji Lanjut Duncan menunjukkan bahwa tidak ada perbedaan nyata antara perlakuan 10, 15, dan 20%, namun nilai kelangsungan hidup tertinggi diperoleh pada perlakuan konsentrasi ekstrak 10% yaitu 56,67% dengan waktu rendaman 2 menit. Kata kunci: ikan nila, Aeromonas hydrophila, daun ketepeng cina iii ABSTRACT The objective of this research was to determine the antibacterial effectivity of Cassia alata L. Leaf extract in curing of Oreochromis niloticus that was infected by Aeromonas hydrophila with dose was 108 CFU/ml. The research was conducted at the Laboratory of Brackish Water Fisheries Aquaculture Development Center, Ujung Batee, Aceh Besar and the chemistry Laboratory of Education and Teacher Training Faculty, Syiah Kuala University from September to December 2014. The research used the Completely Randomized Design with three extract concentrations, three duration treatments and two controls. The extract concentration treatments were 10, 15, and 20% with the duration treatments of 2, 4, and 6 minutes. The negative control was the injection of PBS solution and the positif control was the injection of A. hydrophila without any treatment. The result of ANOVA test showed that the C. alata L. leaf extract gave the effect on the survival rate of O. niloticus that was infected by A. hydrophila at 5% of threshold. The further test of Duncan showed that there wasn’t the significant difference between treatments of 10, 15, and 20%, how ever, the highest survival rate value was obtained at 10% of extract concentration (56,67%) with the treatment duration of 2 minutes. Keywords: Oreochromis niloticus, Aeromonas hydrophila, Cassia alata L.