The present invention relates to a composition for prevention or treatment of sepsis or septic shock, in which the composition includes neoagarooligosaccharide as an active ingredient, and the neoagarooligosaccharide according to 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.