Whey protein is a by-product derived from the production of cheese and it has many benefits for human health that what the recent research work has shown, so it is known as a functional food. It is known that there are salt whey and sweet whey depending on the process of making cheese. Whey protein is absorbed and digested rapidly. Whey protein contains a number of bioactive components including β-lactoglobulin, α-lactalbumin, serum albumin, immunoglobulin, and lactoferrin. These components have positive effects on health such as immune improving and antioxidant characteristic that reduce hypertension, cancer, hyperlipidemia, and virus contagious. The transformation of the amino acid cysteine to glutathione can partially these effects. In addition, whey protein can cure inflammatory bowel disease (IBD). Moreover, whey protein is a rich source of branched chain amino acids, which are particularly good for athletes and sarcopenic cases. In this review, we conclude the characteristics of whey protein and the latest results related the effects of whey protein on specific conditions for human health.