Son of sevenless homolog 1 (SOS1) protein is a ubiquitously expressed adapter. As a key protein in intracellular signaling, SOS1 plays an important role in many signal transduction pathways, such as Ras and Rac signaling pathways. The abnormal expression or mutation of SOS1 is closely related to clinical diseases. In this article, we review research progress on SOS1 functions and its roles in physiology and pathophysiology.