Ecoli infection in the field-scavenging ducks in Tra Vinh province and the antibiotic susceptibility of isolated E. coli were investigated in this study. Laboratory test of 366 internal organ samples collected from the duck flocks in 4 districts of Tra Vinh province showed that the average infected rate of E. coli in the duck flocks was 63.39 percent, with the highest rate from the duck flocks in Cau Ke district (70.07 percent) and the lowest rate in Chau Thanh district (53.13 percent). The infected rates of E. coli in the layer, growing ducks and ducklings were 87.69 percent, 67.27 percent and 47.06 percent respectively. The infected rate of E. coli in the diseased duck flocks was higher than that of the normal ones (71.91 percent and 55.32 percent respectively). Serotyping by slide agglutination test with specific antiserum to different serogroups of E.coli showed that 87.88 percent of isolated E. coli were positive, and the presence of serogroup II (O26 + O119 + O127) and serogroup III (O125 + O126 + O128) was higher than that of serogoup I (O111 + O55 + O26) and serogoup IV (O114 + O124 + O142). The isolated E. coli from the field-scavenging duck flocks in Tra Vinh province were susceptible to antibiotics such as: amikacine, colistine
fosfomycine, ampicillin + sulbactam and most of them resistant to doxycycline, spectinomycine, thiamphenicol.