Technical Abstract: Campylobacter causes human food-borne illness and epidemiological evidence indicates poultry and poultry products as a significant source of human infection. Reducing Campylobacter in the poultry intestinal tract would reduce contamination of poultry products. Caprylic acid, is a medium chain fatty acid reported to be effective in killing a variety of bacterial pathogens, including Campylobacter, but its effect has not been investigated in the control of Campylobacter in preharvest market aged poultry already colonized with this bacterium. The objective of this study was to determine the therapeutic effect of caprylic acid on Campylobacter counts in the cecal contents of 42-day-old chickens. Four trials were conducted. In the first two trials, day of hatch chicks (n=60 per trial) were assigned to six treatment groups (n=10 birds per treatment group): positive controls (Campylobacter, no caprylic acid), 0.7% or 1.4% of caprylic acid in feed for the last 3 days of the trial with or without a 12 hour feed withdrawal. Treatments were similar for Trials 3 and 4 except the doses used were 0.35% or 0.7% caprylic acid supplementation for the last 7 days of the trial. On day 42, ceca were collected and Campylobacter counts determined. The supplementation of caprylic acid at 0.35% and 0.7% consistently reduced (P < 0.05) the colonization of Campylobacter in the chicken ceca compared to positive control treatment. When these treatments were evaluated after a 12 hour feed withdrawal period, 0.7% caprylic acid reduced Campylobacter colonization in the 3 day treatment supplementation. Body weight and feed consumption did not differ between the caprylic acid and control groups. The results suggest that therapeutic supplementation of caprylic acid in the feed can effectively reduce Campylobacter in market aged chickens and may be a potential treatment for reducing pathogen carriage in poultry.