---

Abstract Background and Objectives: gasterointertidis is one of the most common forms of Salmonellosis, which is a worldwide problem. The invasive characteristic of intestinal bacteria is one of their pathogenicity Mechanisms , which can be easily investigated by cell culture technique. In this study ,the invasive characteristic of some Salmonella serogroup were investigated by using HEP-2 cell. Methods and Material: The rectals soap were prepared from 280 diarrhea patients referred to Imam Khomeyni and children medical centres , 140 with bloody diarrhea and 140 with watery diarrhea as a comparison group. The rectal soap was taken before patients taking any antibiotics, and 140 rectal specimens were taken from healthy people as a control group. All the samples were inoculated in differential and selective media, like Hektoen enteric agar and Xylose lysine deoxycholate (XLD) agar .After incubation at 37C for 24 hours, the colonies were examined and identified by conventional biochemical and serological tests. Using HEP-2, cellular invasion characteristic of Salmonella serogroups was assessed. Moreover, the antibiotic resistance patterns were performed according to Clinical and Laboratory Standards Institute (CLSI). Results: Of all tested samples, 35(8.3%) are Salmonella strains. The frequency of Salmonella is reported for bloody diarrhea (5.2%) , watery diarrhea ( 1.7%) and control group( 1.4%) .The most abundant serogroups with invasive characteristic, using HEP-2 cell culture, are serogroup B ( 62.9%) and D (17.2%). Conclusion The results obtained in this study show that the majority of Salmonella isolates are without invasive characteristic. Key words: Salmonella, Diarrhea, Cell invasion, Cell culture