The current study was aimed to detect the existence of genes encode outer membrane proteins: transfer protein (traT) and increased serum survival (iss ) which associated with resistance to complement bacterial lysis activity in different Enterobacteriaceae species isolates .Enterobacteriaceae isolates included in this study were (5) isolates of E. coli , K. pneumonia, Salmonella typhi and Shigella dysentery, (4) isolates of Proteus vulgaris and (2) isolates of Serratia marcescens which were isolated from different clinical infections . The traT and iss genes were revealed from whole DNA of 26 isolates of Enterobacteriaceae family, it was found that 21(80.7%) of Enterobacteriaceae isolates gave positive result for traT gene at 288bp while only 17(65.3%) of isolates gave positive result for iss gene at 258bp. It was observed that the traT gene was recognized among 100 % of Salmonella typhi and Serratia marcescens strains and the prevalence of a traT gene was showed among 80 % of K. pneumoniae and Shigella dysentery isolates whereas 75% of Proteus vulgaris and 60% of E. coli isolates contain the traT gene. The iss was found among 80% of both E. coli and Shigella dysentery isolates while it was observed in 60% of K. pneumonia and Salmonella typhi isolates and it was present only in 50% of Proteus vulgaris and Serratia marcescens isolates, as conclusion the study confirmed presence of traT and iss which linked to human complement resistance among local Enterobacteriaceae species and high rate of occurrence among extraintestinal isolates.