The present invention relates to a composition for selectively detecting an extremely small amount of peptidoglycan in sample, a preparation method of the composition, and a detection kit for peptidoglycan. It is possible to quantify a small amount of peptidoglycan contained in human blood, tissue, body fluid, water or food, and to diagnose an infection of microorganism with peptidoglycan as a component of cell wall using the composition and the detection kit. In addition, the composition can be applied for a diagnosis reagent of detecting an infection of Gram-positive bacteria in animal or human being in advance, and thus, can be used for the prevention or treatment of food poisonings and bacterial sepsis.