The results presented here show that dietary MOS supplementation at the levels of 1 and 1.5 g/kg increased egg production performance and feed efficiency in aged laying hens. This improved performance could be largely attributed to the increased ileal nutrient digestibility and reduced pathogenic intestinal bacteria, as microbiological data showed that supplemental MOS decreased ileal population of Salmonella. From the present findings, it seems that supplemental MOS could improve antibody production titer against different viral and non-viral antigens. The potential of MOS for promoting immune responses and preventing disease occurrence, however, needs further investigation.