The present study was conducted to investigate biochemical, serologic, and pathogenic characteristic of E. rhusiopathiae isolated from the cases of acute septicemic swine erysipelas in Youngnam provinces during the period from June 1988 to September 1990. The majority of biochemical and cultural properties of E. rhusiopathiae isolated from pigs affected with acute erysipelas were identical to those of the standard strain employed. All of the 45 isolates were serotype la. All isolates were highly susceptible to penicillin G, lincomycin, cephalothin, ampicillin, erythromycin (MIC : 0.025-0.78IU or ${mu}g$ / ml ), and moderately susceptible to oleandomycin, oxytetracycline, chloramphenicol (MIC : 0.78-25${mu}g$ / ml ). Kanamycin and sulfadimethoxine showed no activity against the isolates(MIC : ＞400${mu}g$ / ml ). The MICs of dihydrostreptomycin presented two distribution peaks ; of 45 strains, 5(11.1%) were resistant to dihydrostreptomycin(MIC : 400${mu}g$ / ml ). All of 5 selected isolates were pathogenic for mite and $LD_{50}$ was $3.7{ imes}10^3$viable cells. Mice immunized subcutaneously with live vaccine did not die after challenge to virulent isolates of E. rhusiopathiae.