Abstract: Six isolates of Erwinia carotovora were isolated from naturally infected potato tubers in different localities in Egypt. The isolates were tested pathologically, morphologically and serologically. All E. carotovora isolates exhibited the same results in the morphological and pathological tests and identified as E. carotovora. The isolates showed variation in their virulence. The serological tests such as Crossed Immunoelectrophoresis (CIE) and Double Gel Diffusion (DGD) were used to study serological differences between E. carotovora isolates. The serological differences between E. carotovora isolates using CIE were clearer than in DGD, since the numbers of precipitin peaks detected in the homologous and heterologous reaction were almost twice than the numbers of precipitin bands in DGD. The obtained results using CIE with E. carotovora isolates were emphasized by reciprocal analysis procedure. The common and specific antigens for each isolate were clearly detected. At least five antigens were found to be common among E. carotovora isolates. One and two antigens were found to be specific to E. carotovora isolates No. 1, 2 and 4, 5, respectively, while four antigens were found to be specific to E. carotovora isolate No. 6. No antigens were found specific to E. carotovora isolate No. 3.