Technical Abstract: Salmonella Enteritidis and Campylobacter jejuni are two major food-borne pathogens in the US, accounting to more than 3 million cases of human illness annually. Chickens are the natural hosts of these bacteria and their drinking water can be a potential source of Salmonella and Campylobacter resulting in the colonization of birds. In this study, trans-cinnamaldehyde (TC), a natural, GRAS ingredient in cinnamon oil was evaluated for its efficacy to inactivate Salmonella and Campylobacter in the drinking water of chickens. Well water containing 0, 0.016, 0.03 and 0.06% TC were inoculated with a five-strain mixture of Salmonella or Campylobacter. Water samples containing 1% chicken feces or feed were also included. The samples were incubated at 12.5 or 25C for 7 days, and analyzed for bacterial population on days 0, 1, 3, 5, and 7. Duplicate samples of treatments and control were included, and the study was replicated three times. Trans-cinnamaldehyde at 0.06% inactivated Salmonella completely after 24 h in water with 1% feces at both temperatures, relative to controls. In water containing 1% feed, TC (0.06%) reduced Salmonella to undetectable levels after 3 days at 12.5C or 7 days at 25C. Presence of feed or feces in water reduced the antibacterial effect of TC. The effect of TC on Campylobacter was more pronounced than that on Salmonella. TC at 0.06% completely inactivated the pathogen after one day of incubation at both temperatures. The presence of feces or feed did not have any effect on the antibacterial property of TC Campylobacter. Results indicate that TC is effective in killing Salmonella and Campylobacter in chicken drinking water, and could potentially be used to control these pathogens in chickens through the drinking water on farms.