The present experiment was carried out to determine the effects of dietary organic acid supplementation (0.5, 1.0, and 1.5%) on performance (body live weight, feed intake, feed efficiency, and egg production), egg quality and blood parameters in laying hens. A total of 20 week old 180 Lohmann LSL white layer hens which were divided into 4 groups each containing 45 hens. The hens were fed with diets (17% crude protein and 2800 kcal/kg metabolic energy) supplemented with 0% (control group), 0.5% (group I), 1.0% (group II), 1.5% (group III) organic acid mixture (formic and propionic acids, and their ammonium salts) during 18 weeks. The dietary organic acid supplementation did not significantly affect growth performance (body weight, food consumption) and egg quality parameters. But this treatment markedly improved the egg production, by accelerating the laying capacity and prolonging the laying period in 24-28 week old and 36-38 week old hens respectively and the feed efficiency at a lesser extend. Serum total protein (p<0.01) and albumin concentrations (p<0.05) as well as AST activity (p<0.05) were significantly increased, whereas the other tested serum parameters (ALT activity and cholesterol, HDL, triglyceride, VLDL and total lipid concentrations) were unaffected. From these results, it was concluded that dietary supplementation with organic acids and their salts could be used in layer hens with benefit on egg production and protein metabolism efficiency.