Abstract: isolates of Pseudomonas solanacearum in sweet potatoes were obtained from 5 provinces of Fujian,Guangdong,Jiangxi,Jiangsu and Zhejiang.The tests of host range,infiltration and melanin formation showed that 63 isolates could infect tobacco and eggplant, but could not infect hanana.The infective ability was related to the pathogenicity of isolates.The tobacco leaves infiltrated by the isolates could caused necrotic spots in 24～60 hours.The isolates inoculated in the Ltyrosine medium could produce rnelanin.The division of physiological races was discussed.