Fish fauna survey biodiversity was conducted in Ujung Kulon National Park, Pandeglang-West Java, to reveal fish diversity in mangrove ecosystem. Samples were caught using electrofish (12 V 10A), gill net (mesh sized 1-1.5 cm) and fishing tackle. Result showed that there were 58 fish species belongs to 34 families and 43 genera gobiidae was a dominant famili with 3 species. Cigenter river has highest diversity with H = 2.74, E=0.930, d = 5.346. Serinding fish (Ambassis dussumieri) was the highest abundance compared to others.