The objective of the present study was to evaluate the antimicrobial effect of short and medium fatty acid chain. Total number of 2000 Cobb broiler chicks (mixed sexes) were commercially purchased from EL Dakahlia poultry company that were 1d old were reared up to 40d of age. Corn and soybean meal based starter and grower diet were supplemented. Chicken were randomly divided in to two main group, 1st group act as normal control, 2nd group was add C12( mixed short and medium fatty acid) in drinking water for 3 day each 8 day at 11, 22 and 33 days age. Blood sample were collected before and after taking C12 treatment for biochemical examination. Supplementation of C12 caused decrease in serum level of AST, ALT, glucose, cholesterol, triglyceride, and pro-inflammatory cytokines as IL-6, increase HDL and total protein. Evaluation of antimicrobial activity of C12.