Abstract: The outer membrane patterns of 130 pathogenic E. coli strains isolated from ducks of 3 provinces or municipal cities in southwest China were determined in this study. Among these 130 strains, 53 isolates belonged to prominent serotype O93, O92, O78 and O76, while 77 strains were serotype O46 and other serotypes. There were 4 different OMP patterns among all strains tested. 62.3% (81/130) of strains that belong to 29 serotypes were identified to be OMP-1， including O93，O92，O78 and O76, suggesting that OMP-1 was the main OMP pattern. Subsequently, a pair primers for amplification of ompA gene was designed according to sequence of the E. coli K-12 available in GenBank. The ompA gene were then amplified and sequenced from 9 prominent serotype strains and 1 serotype O46 strain. Sequence analysis revealed that the ompA gene of all 9 prominent serotype strains was 1 171 bp long and composed of only one large open reading frame (ORF) with a size of 1 053 bp, which encoded a protein consist of 350 amino acids, proompA. The first 21 amino acids encoded a signal peptide and the mature OmpA protein was composed of 329 amino acids. The ORF of ompA gene from O46 serotype strain was 1 041 bp in length with a 12 bp depletion at the site of 400-411 bp compared to other serotype strains, and the mature OmpA protein contained 325 amino acids. It was also found that the nucleotide sequences of ompA genes hared high homology with an identity ranging from 95.8% to 100% among 10 pathogenic E.coli strains from ducks.