The present invention relates to a composition comprising neoagarooligosaccharide as an active ingredient, for prevention or treatment of sepsis or septic shock, and the neoagarooligosaccharide of the present invention has an excellent effect in terms of immune enhancement by effectively suppressing inflammation, and also exhibits a good effect in preventing sepsis, and therefore can be effectively used in pharmaceuticals and functional foods for prevention or treatment of sepsis or septic shock and immune enhancement.