A prebiotic is defined as an indigestible feed substance that beneficially affects the host by selectively stimulating the growth and/or activity of one or a limited number of bacteria in the large intestine, thereby improving host health and products. This study was conducted to determine the effects of supplementing prebiotic fructooligosaccharide (FOS) to the diets of Hy-Line W-36 laying hens. A total of 168 Hy-Line W-36 laying hens were allocated to four dietary levels of FOS (0, 1.0, 2.0, 3.0g/kg diet), 6 replicates of 7 birds each during 63-74. The experiment was performed using a completely randomized design. Productive performance was not significantly affected by the FOS supplementation. Body weight gain was linearly decreased with increasing FOS levels in the diet (p<0.01). However, eggshell strength, shell thickness and Ca and p percentages were not significantly affected, as were anti-sheep red blood cell titres, blood parameters and blood metabolites. In the first period of the experiment (63-65weeks), shape index and Haugh unit at the dose of 3.0g/kg FOS were significantly increased and decreased in comparison with control, respectively (p<0.05). In the third and fourth periods (69-71 and 72-74 weeks of age), the FOS had no significant effect on the internal egg quality traits. Furthermore, FOS had a linear decrease in the most saturated fatty acids (SFAs), including myristic, palmitic, margaric and stearic fatty acids; some of the mono-un-SFA (MUFA; palmitoleic and ginkgolic acids), and poly-unsaturated fatty acids (γ-linolenic and eicosatrienoic). Supplementing different levels of FOS to the diet of commercial laying hens had no significant effect on the layers' performance, immune response and blood parameters, whereas there was a significant effect on some of the internal egg quality traits and egg yolk fatty acid contents.