Interleukin-4 (IL-4) is a basic immunoregulatory cytokine in T helper 2 (Th2)-mediated immune response. It has a complex signaling system and multiple functions. In terms of brain tissues, many studies have showed that IL-4 can protect cognitive function in inflammation. This article summarizes the evidence and mechanism of action of IL-4 in protecting cognitive function, as well as the pathway and evidence for IL-4 protecting cognitive function in Alzheimer's disease, ischemic cerebrovascular disease, and postoperative cognitive dysfunction.