This study was conducted from September 2006 to September 2007 to identify major pathogens, especially bacteria, of diseased frog (Rana tigerina) farmed in the peri –urban area of Ho Chi Minh City. Challenge of cultured frog with Aeromonas hydrophila. That were isolated from diseased frogs with clinical signs of ulcerative syndrome were carried out. Experimental frogs were injected on the vetral left thigh with a variety of bacterial concentrations. Average 18-25g sized frog (Rana tigerina) were stocked at 10 frogs/tank. ...