Introduction: Salmonella is a gram-negative intestinal microorganism that causes food poisoning in humans. The genus Salmonella has five virulence genes stn, Phop / Q, spvc, slyA and sopB. These genes encode proteins in different parts of the bacterium that can counteract the immune system, complement, and death within the cell. The aim of this study was to identify virulence genes in Salmonella typhimurium strains isolated from clinical specimens using Multiplex PCR and to determine their antibiotic resistance patterns. Materials and Methods: In this descriptive cross-sectional study, 60 stool specimens were collected from the patients with acute diarrhea and vomiting in Karaj hospitals and hospitals during 2017. Antibiotic susceptibility test was performed on Muller Hinton agar medium (CLSI). Multiplex PCR was also performed to detecting virulence genes using specific primers. Results: The results of antibiotic susceptibility test showed that all isolated samples were susceptible to imipenem, gentamicin and amikacin. Also, the frequency of Phop/Q, slyA and stn genes were 100%, 98.3% and 91.6%, respectively. Also, sopB and Spvc genes were not detected in Salmonella typhimurium isolates. Conclusion: The results of the present study indicate on the high incidence of virulence genes in Salmonella typhimurium clinical samples which can be considered as an alarm signal for the spread of these genes to other Salmonella serotypes.