In this study, we examined the effects of formic acid administration to the drinking water on performance, intestinal microflora and carcass contamination in male broilers. A total of 312 day-old male broiler chicks were allocated to two groups with three replicates. The first group (control) received normal drinking water (pH 7.4) during the experiment. The second group consumed acidified drinking water (pH 4.5) after 5 d of age. At 43 d of age, twelve birds were randomly selected from the control group to determine the effect of acidified drinking water on carcass contamination. These birds were only given normal or acidified (pH 3) drinking water for 8 h prior to slaughter. The reduction of water pH from 7.4 to 4.5 significantly decreased body weights of male broilers at 21 and 42 d of age. However, no differences were observed between male broilers given normal and acidified drinking water in terms of feed intake, feed conversion ratio and mortality. The pH value of the gizzard contents was not significantly affected by acid water treatment. There were no significant differences in the intestinal population of E. coli, total organism and Salmonella between the groups. The total organism and E. coli counts of the carcass slightly decreased in the acidified group. No Salmonella was identified in carcass samples of any of the treatment groups. The results showed that drinking water acidification did not provide beneficial effects on performance, intestinal microflora and carcass contamination in male broilers.