A gram-negative bacillus was isolated from the bodies of dead clams among clambanks along the south beach of Jiangsu province. It was confirmed to the Vibrio furnissii by morphological and biochemical characteristic examinations. This isolate grows well in clam's body fluid media and may multiply rapidly in sea-water at temperature about 25—37℃. It is of high toxicity. The healthy clams were all diseased with the same syndrome and died as natural illness by inoculate them with the isolate. It is considered that the large enormous death of clams along the south beach of Jiansu province is concerned with the wide spreading of the clam's infectious disease caused by Vibrio furnissii which hasn't been reported both internal and abroad.