Abstract: A bacterium which isolated from prawn nursery wastewater in Qionghai,Hainan Province in August -005,was maintained by our laboratory and named Bdh5221.According to previous study,Bdh5221 could prey most Gram-negative bacterium and can also be cultivated by using heat-killed Gram-negative bacterium.In the present study,morphological,physiological characteristics,drug sensitivity,and 16S rDNA sequence of Bdh5221 were analyzed.The morphological studies showed that the strain Bdh5221 were Gram-negative,motile and had a bacilliformor bacilliform shape with flagellum at one side,which size was mostly(0.-- 0.5) μm ×(0.6- 1.5) μm.The physiological characteristics showed that this bacterium were catalase-positive,oxidase-negative,gelatin colliquation-positive and sensitive to the vibriostratic agent O/1-9.Drug sensitive results indicated that this bacterium were enrofloxacin-positive,neomgcin-positive,biograncetin-positive,penicillin-negative,Sulfadiazine-negative and vancocin-negative.16S rDNA gene of Bdellovibrio sp.Bdh5221 was 99% similar with a navel marine bacterium Kordiimonas gwangyangensis.The similarity with all recognized Bdellovibrio-and-like organisms was from 90% to 70%.It indicated that the bacterium might be a novel Bdellovibrio-and-like organisms.