Pasteurella multocida is a pathogenic, Gram-negative bacterium that is commonly found as normal flora in nasopharynx of variety of wild and domestic animals. Numerous virulence factors have been described for P. multocida isolates which include adherence and colonization factors, iron-regulated and acquisition proteins, extracellular enzymes such as neuraminidase, lipopolysaccharide (LPS), capsule and a variety of outer membrane proteins (Omp). OmpA has a significant role in stabilizing the cell envelope structure by providing physical linkage between the outer membrane & peptidoglycan. It has been shown to mediate P. multocida -host cells interaction via heparin and/or fibronectin binding and therefore act as an important invasive molecule which could determine the final outcome of initial infection. Comparative nucleotide sequence analysis of ompA gene of P. multocida has revealed that despite extensive genetic diversity in ompA of P. multocida, most sequences could be classified into two major allele classes namely ompA allele (I) and allele (II). The P. multocida recovered from nasal cavity of bovine and belonging to two ompA classes were tested for their differential virulence. In vitro pathogenicity studies on Madin Darby Bovine Kidney (MDBK) cell line employing adhesion and invasion assays indicated that P. multocida strain with ompA (I) is more invasive than P. multocida strain with ompA (II). In vivo studies in mice further reiterated that the isolates harbouring ompA(I) were comparatively more virulent to isolates harbouring ompA (II).