One hundred and twenty diarrhea samples were collected from different hospitals in Baghdad, four isolates (3.3%) (PI ,P2,P3,P4) were obtained and identified as Plesiomonas shigelloides from these samples. Four isolates ere-also-obtained and identified as the same bacteria from the environmental samples, two isolates (10%) from twenty water samples (termed W1,W2) and two isolates (10%) from twenty fish samples (termed F1,F2). Investigation of antibiotic susceptibility was done for all isolates. Results showed that all (8) isolates were resistant to ampicillin, carbenicillin, penicillin, cioxacillin and streptomycin, while seven isolates were resistance to pipracillin and ticarcillin, six isolates were resistant to vancomycin and five isolates were resistance to tetracycline. All isolates were sensitive to amikacin, cefotaxime, ciprofloxacin, gentamicin, naldixic acid, tobramycin, norfloxacillin, rifampicine and trimethoprime . Some of the virulence factors were determined in this bacterium, and the results showed that all isolates were produced lecithinase, proteinase and B- haemolysin enzyme, but they werenot produced gelatinase ,DNase and amvlase. However, six isolates showed ability to produce (3- actamase, while Fl and P4 isolates could not produced this enzyme. Two isolates (Fl and \W2) only don't have ability to produce lipase enzyme. Ability of bacterial isolates to adhesion on epithelial cells was studied as one of important virulence factors, it was found that all isolates have the ability to adhesion on living and non-living surfaces. The plasmid profile for all isolates was studied, and the results showed that the plasmid profile was similar for all isolates. All isolates contained two small plasmid DNA bands approximately in the same sizes. The role of plasmicls in pathogenicity of P. shigelloides PI were studied, throughout cure this isolate using SDS. Results indicated that number (9%) of cured strains were obtained, which lost their ability to resist number of antibiotics. These strains were investigated determine whether they have lost other virulence factors. Results indicated that all cured strains lost their ability to hydrolyze casein, seven strains lost their ability to produce (B- lactamas and (B-haemolysin, while non of these strains lost their ability to produce lipase and lecithinace. These results indicated that the trait of (B- lactamas, haemolysin and proteinase production in addition to resistance trait for tetracycline and streptomycin were plasmids born. While the lipase and lecithinase production trait were chromosomal born in Plesiomonas shigelloides PI.