Abstract: Skin Ulcer Disease (SUD) is a new disease in Schizothorax prenati. The purpose of this study was to elucidate the etiology of SUD in recent outbreaks in Sichuan province, China. One dominant bacteria (D060501) was isolated from the diseased Schizothorax prenanti with typical skin ulcer. It was identified as Aeromonas hydrophila by morphological features, physiological and biochemical characteristics and 16S rDNA sequence. The bacterium was very sensitive to chloramphenicol and gentamicin and resistant to tetracycline, SMZ, doxycycline and carbenicillin. The virulence of the bacteria to Schizothorax prenanti was checked by challenged experiment.