Technical Abstract: Campylobacter is one of the most common causes of foodborne illness, and poultry is considered a primary source of Campylobacter infections. Caprylic acid, an eight-carbon fatty acid, has been shown in previous studies to reduce enteric cecal Campylobacter concentrations in poultry when administered in the feed. For greater ease of application for producers, a water soluble form of caprylic acid, sodium octanoate, was evaluated for efficacy against enteric Campylobacter. The first trial consisted of 84 birds in 7 groups (n=12/group): an untreated control and 6 other groups, all of which were inoculated with Campylobacter and received 0%, 0.175%, 0.35%, 0.7%, 1.4%, or 2.8% water soluble caprylic acid in water 3 d prior to necropsy on the 14th d of the trial. The second trial consisted of 96 birds in 8 groups (n=12/group): an untreated negative control and seven other groups, all of which were inoculated with Campylobacter and received 0%, 0.044%, 0.088%, 0.175%, 0.35%, 0.7%, or 1.4%, water soluble caprylic acid for 3 d prior to necropsy on the 14 d of the trial. Chicks were challenged at d 3 with C. jejuni, 2.1x107 or 1.2x104 CFU/mL in trial 1 or 2, respectively. In trial 1, only the 0.175% dose caused a significant reduction in cecal Campylobacter counts in comparison with the positive control (approximately a 2 log reduction). In trial 2, there was no significant reduction in C. jejuni among any of the groups in comparison with the Campylobacter positive control. Unlike caprylic acid in feed, which is effective, water treatment with caprylic acid had an inconsistent effect on intestinal Campylobacter counts.