Mammalian milk or colostrum usually contains, in addition to lactose, a variety of neutral and acidic oligosaccharides. Although the oligosaccharides of human milk have been reviewed in several recent publications, those of non-human mammals have received much less attention. This paper reviews the chemical structures and the variety of milk oligosaccharides in species other than humans, including placental mammals (e.g. primates, domestic herbivores, bears and other carnivores, the rat and the elephant) as well as monotremes (platypus and echidna) and marsupials (e.g. wallaby). The gastrointestinal digestion and absorption and the possible biological functions of these oligosaccharides are also discussed.