The effects of different levels of an eubiotic on laying performance, egg quality parameters, serum enzymes and antioxidant levels, and egg yolk fatty acid composition were examined in the present study. Six diets were formulated to contain 0, 200, 400, 600, 800 and 1000 mg/kg EFA. Each diet was randomly fed to a group of 24 hens for 10 weeks, housed in 6 separate cages (4 hens per cage).