Abstract: Background and Objective: Campylobacteriosis is a significant health problem worldwide and poultry are considered as one of the main vehicles of transmission. This study was conducted to determine whether alum reduces Campylobacter colonization in broilers by reducing horizontal transmission between birds or by reducing Campylobacter counts in birds already colonized (Therapeutic efficacy). Materials and Methods: Two replicate experiments were conducted and in each experiment, day of hatch broiler chicks (n = 295) were divided into 7 treatment groups including controls. Each treatment was reared in either no (0 kg), low (0.78 kg m–2) or high (1.58 kg m–2) concentrations of aluminum sulfate (alum; Al+ Clear). During days 7, 14, 28 and 42, ten birds from each treatment were analyzed for Campylobacter counts in the ceca. To evaluate whether alum inhibits horizontal transmission between birds, Campylobacter negative birds were reared with seeder birds that served as carriers. Results: Alum reduced (p<0.05) horizontal transmission of Campylobacter at 14 and 28 days in experiment 1 and only with the highest concentration of alum at 42 days in experiment 2. To evaluate the therapeutic efficacy of alum, all birds were inoculated with Campylobacter (5.2×106 CFU mL–1) prior to placement in pens. Infected birds reared on low or high alum had lower (p<0.05) Campylobacter counts at 14 and 28 days in only 1 of 2 experiments. At 42 days, there were no differences in cecal Campylobacter counts between alum treated and untreated controls in experiment 1 and for only the highest concentration in experiment 2. Conclusion: It appears treating litter with alum is not a consistent way to reduce enteric Campylobacter counts.