The members of the Srcfamily kinases are Src, Lyn, Fyn, Yes, Hck, Lck, Fgr, Blk, and Yrk. Each of these have a common structure consisting of an unique domain at the N-terminal, followed by SH3, SH2 and tyrosine kinase domains. In immume cells, the Src-family kinases play roles as critical regulators of a large number of intracellular signaling pathways, including integrin signaling pathway. Integrins are major cellular receptor that mediate cell to cell and cell to substratum interactions. Src is expressed ubiquitously, however the expression level is higher in brain, osteoclasts, and platelets. Src plays a role in cell adhesion, cell morphology and motility, and bone resorption. Src contains a 14-carbon myristoyl group attached to an SH4 domain, a unique domain, an SH3 domain, an SH2 domain, an SH2-kinase linker, a protein–tyrosine kinase domain (the SH1 domain), and a Cterminal regulatory segment. One of the two most important regulatory phosphorylation sites in Src is Tyr527. Under basal conditions in vivo, 90–95% of Src is phosphorylated at Tyr527, and phosphotyrosine 527 binds intramolecularly with the Src SH2 domain. Tyrosine 416 is present in the activation loop and its phosphorylation promotes kinase activity.