Abstract: In 2011, there was an outbreak in a Plectropomus leopardus farm in Wenhui Town, Yandui Village, Hainan Province. The color of sick fish turned white and the tail fin festered. We isolated a Strain X11YD05 from sick P.leopardus which was proved to be pathogen by artificial infection and the LD50 was 1.67105 cfug-1 in Epinephelus coioides using Karber method. To determine the molecular characteristics of X11YD05, we amplified the16S rDNA, transmembrane regulatory protein (toxR), RNA polymerase 70 factor (rpoD), actin-like cytoskeleton protein (mreB), topoisomerase (topA) and replication origin-binding protein (rctB) by PCR. Sequence analysis indicates that X11YD05 belonged to V.harveyi. Drug sensitivity test shows that X11YD05 was sensitive to norfloxacin, ofloxacin, ciprofloxacin, enrofloxacin and cotrimoxazole.