Abstract: In the present study, we investigated the effect of Microencapsulated-Inulin (MCI) in feed on the improvement of the growth performance in broilers using MCI prepared from Korean Jerusalem artichoke as a natural antibacterial growth promoter. After sex identification, 320 male Ross 308 broilers were randomly allotted to treatment groups and fed for 35 days. Treatment groups consisted of T1 (no supplementation; control), T2 (avilamycin, 8 g ton^-1), T3 (MCI, 200 g ton^-1) and T4 (MCI, 250 g ton^-1). The growth performance and the dressing percentage were higher in broilers in groups T3 and T4 than in broilers in groups T1 and T2; statistical significance in the differences among the treatment groups was verified. The weights of breast and thigh muscles were significantly higher in broilers in T3 and T4 than in T1 and T2 and abdominal fat was significantly lower in broilers in T3 and T4 than in T1 and T2 with a decrease of 19.08-23.30%. The levels of blood immunoglobulins, IgG, IgM, IgA and weights of thymus and bursa of fabricius were significantly greater in T3 and T4 compared with T1 and T2 with an increase of IgG, IgM and IgA being 125.1-168.5, 100.5-170.5 and 103.0-125.3%, respectively. The colony counts of the beneficial intestinal microorganisms, Bifidobacteria and Lactobacillus were significantly greater in T3 and T4 than in T1 and T2 but the counts of harmful E. coli and Salmonella were significantly less in T3 and T4 than in T1 and T2. The supplementation of broiler feed with 200 g ton^-1 microencapsulated-inulin can significantly improve the productivity of broiler chickens.