The main objective of the study was to investigate the effect of two types of organic acids (formic acid, FA and citric acid CA) on performance, blood parameters, immune response and bacterial count. A total number of 250 unsexed 7 d old ducklings (Cairina Moschata) were randomly divided into five dietary treatment groups, 50 birds each in five equal replicates. The first group was fed a commercial basal diet without supplementation (control), the 2nd and 3rd groups were fed basal diet supplemented with 0.5 and 1.0 % of FA, while the 4th and 5th groups were fed basal diet supplemented with 2.0 and 3.0% CA. Body weight (BW), body weight gain (BWG), feed conversion, some carcass characteristics and economic efficiency were determined. At the end of the experiment (70 d), blood samples were collected to determine some blood constituents. In addition, bacterial counts of the digestive system were measured. Results showed that duckling fed the basal diet supplemented with organic acids had significantly greater BW, BWG, economical efficiency and better feed conversion as compared to control. All dietary supplements decreased serum AST, ALT, urea, creatinine, total lipids, triglycerides, cholesterol, LDL and increased T3, T4, TAC, GSH, GPX, SOD, glucose, total protein, globulin, γ-globulin, IgA, IgM, IgG, LA, BA, LTT, phagocytic activity, phagocytic index, RBCs and hemoglobin as compared to control. Dietary supplementation of organic acids increased dressing percentage and total edible parts compared to control. Moreover, supplementation of either formic or citric decreased total bacterial count, Salmonella, E.Coli and proteus spp. compared to control group. In conclusion, either formic or citric acid could be used safely as natural growth promoters to improve growth and immune response of duckling.