Abstract:High performance liquid chromatography and mass spectrometry were employed to analyze the composition of bound sialic acids in human，bovine，and goat milk.Then，the gastrointestinal digestion process of infants was simulated to study the digestive characteristics of lipid-bound，protein-bound，and oligosaccharidebound sialic acids，and the digestibility of different bound sialic acids in the three kinds of milk was compared.The sialic acids in human milk were mainly oligosaccharide-bound N-acetylneuraminic acid （Neu5Ac），with the content of 734.65 μg/mL and the highest digestibility of 6.13%.The sialic acids in bovine and goat milk were mainly bound to protein，while their digestibility was low，only 0.24%-1.53% and 0.08%-0.70%，respectively.The digestibility of lipid-bound sialic acids in human，bovine，and goat milk was high，peaking at 19.78%，38.07%，and 4.60%，respectively.However，due to the low content of lipid-bound sialic acids in the three kinds of milk，there were few free sialic acids dissociated after digestion.In general，there were only small amounts of free sialic acids dissociated from bound sialic acids in human，bovine and goat milk after digestion.