A total of 100 apparently healthy Hubbard chicks, one day of age were used in this study to investigate the effect of formic acid on body performance. |Biochemical and histopathological changes beside its effect on intestinal bacterial growth in broiler were also studied. Cloacal swabs were collected from all chicks for bacteriological examination at day one of age. Eighteen chicks were positive and the distribution of the bacterial agents was 13 for single infection (E. coli, Corynebacterium species and Salmonella species) and 5 in case of mixed infection (Streptococcus, Corynebacterium species, Staphylococcus aureus and E. coli). Serological identification of the isolated E. coli revealed O78 (4) and O157 (2), while, the obtained Salmonella serotypes were S. Typhimurium (3) and S. Enteritidis (1).  Sixty bacterial free chicks were divided into 3 groups (20 birds, each), 1^st group served as control. The 2^nd and 3^rd groups received 1 ml and 2 ml formic acid/ liter drinking water, respectively for 30days. Formic acid in both doses induced a significant increase in body weight gain, total proteins, albumin and globulins coupled with significant decrease in total lipids, cholesterol and triglyceride. Meanwhile, A/G Ratio calcium, phosphorous, magnesium, zinc, sodium and potassium insignificantly increased beside insignificant decrease in liver enzymes (AST, ALT and ALP) uric acid, creatinine and intestinal bacterial content as well as improved the feed consumption and feed conversion rate. Histopathologically, spleen and bursa showed hyperplasia of lymphocytes in white pulp. Hepatic tissue particularly the 3^rd group had mild fatty changes and hydropic degeneration. Also renal tubules of undergo mild hydropic degeneration. In conclusion the use of formic acid as feed additive in chicken broiler ration may act as growth promoter and exhibits positive impact on biochemical parameters, intestinal and immune organs histology beside reduction of colonization of bacteria in intestinal wall.