FRS3 or fibroblast growth factor receptor substrate 3 is a peripheral plasma membrane protein that is a substrate for the fibroblast growth factor receptor. During FGF or NGF stimulation, FRS3 becomes tyrosine phosphorylated and then serves as a platform for the recruitment of multiple signaling proteins for activation of the Ras-MAP kinase signaling cascade. FRS3 is mainly expressed in fibroblast and myoblast cell lines and undergo robust tyrosine phosphorylation in response to several mitogenic ligands. Through interaction with Rho family of small GTPases, FRS3 has been implicated in the reorganization of the actin cytoskeleton and subsequent morphological changes in various cells.