COLIBACILLOSIS is known as a fatal bacterial disease resulting in a high level of commercial loss worldwide. This study amid to elucidate the sequence, genetic characteristics, and phylogeny of the bor gene in Escherichia coli (E. coli) strain c1378 (O78: K80) isolated from AVIAN COLIBACILLOSIS in Iran and develop a rapid and optimal polymerase chain reaction (PCR) molecular-based technique with specific primers to detect this gene in E. coli. A virulent AVIAN E. coli (i. e., laboratory designation E. coli strain c1378) isolated from a chicken with systemic COLIBACILLOSIS from a broiler farm in Tehran, Iran, in 2004 was used as a source of the bor gene. After DNA extraction, PCR method was used to amplify the bor gene. A 658 bp fragment of the bor gene was amplified, sequenced, blasted, and phylogenetically studied. The most similar sequences to the bor gene in E. coli strain c1378 were E. coli APEC O78, Enterobacteria phage HK630, and Escherichia coli BW2952, respectively. There was a high similarity between the bor gene in E. coli bacteria with their phage and plasmid. Moreover, a high similarity was observed between the bor and iss genes (approximately 92%) showing that they were homologous genes. In addition, the similarity analysis of different bacterial species, as well as their plasmid and bacteriophage, to the bor gene indicated that the highest similarity to O78: K80 was related to Paracoccidioides brasiliensis, Bacillus thuringiensis CT43 plasmid pBMB0558, and Salmonella enterica subsp. enterica serovar Kentucky strain CVM29188 plasmid, respectively. Altogether, the results of the present study confirmed the presence of the bor gene in the studied isolates and clarified its sequence, phylogenetic relationship, and similarities of E. coli strain c1378 (O78: K80) isolated from AVIAN COLIBACILLOSIS.