Bdellovibrio bacteria BDF-H16 was isolated from the gut of Carassius auratus gibelio with Aeromonas sobria.Its shape was ob- served by light microscopy,phase-contrast microscopy,electron microscopy and some of its biological characteristics were also studied.It was demonstrated that BDF-H16 was an gram-negative bacterium and had a bacilliform or arc bacilliform shape with a flagellum at one end.Its size was mostly 0.2μm～0.5μm×0.8μm～1.2μm.It had a wide prey area and could lyse all tested gram-negative bacteria and some gram-positive bacteria. The best lysis conditions to Escherichia coli were 6.75×10⁹cfu/mL of prey bacteria concentration、pH7.0~7.5、28℃. It could grow in the solid culture added 0.85%~5.00% NaCl and was inhibited by enrofloxacin and norfloxacin.