Milk is a specialized substance secreted by the mammalian mammary gland and is the material basis for the survival and development of mammals. Understanding the similarities and differences in the milk composition of humans and domesticated mammals and gaining deeper insights into the characteristics of different mammalian milks will help in the targeted development and promotion of different mammalian dairy products. In this review, we summarize the main nutritional components in different mammalian milks and compare the composition and content of protein, fat and lactose, finding that there are large differences in these milk components. Besides, we review the functions and applications of different mammalian dairy products according to the conclusions drawn from the comparison.