Salmonella is still a source of threat to poultry production. In this study, trials for Salmonella isolation from poultry were conducted at Ismailia Governorate, Egypt. The broilers were subjected to clinical, postmortem and bacteriological examinations. On the other hand, the current study of discovering antimicrobial compounds in all fields of microbial control has stimulated research on the antimicrobial properties of plant compounds. The in vitro study was carried out to estimate the antibacterial activity of thymus vulgaris oily extract against Salmonella Typhimurium isolated from broiler chickens suffering from diarrhea. The obtained results indicated that thymus vulgaris oily extract was effective against Salmonella Typhimurium. The in vivo study was established to investigate itsefficacy against experimentally induced salmonellosis in broiler chickens. The obtained findings displayed that thymus vulgaris oily extract was able to reduce the mortalities from 30% in infected non -medicated group to 15% in infected groups treated with thymus vulgaris oily and zero% in groups treated with ciprofloxacin. All infected treated groups showed a greater reduction in clinical symptoms and postmortem lesions severity. The hematological findings revealed an increase in lymphocyte count in group 2 and group4. The biochemical study displayed that treatment of infected groups by thymus vulgaris oily extract and ciprofloxacin induced an improvement in both liver and kidney functions as compared to infected un-medicated group. Our results suggest that the addition of thymus vulgaris oily extract to the drinking water could be effective in decreasing salmonella infection in chickens by increasing the immune response of chicken.