The proto-oncogene tyrosine-protein kinase Src is a key ele- ment of signaling cascades involved in the invasive and meta- stasis-forming capacity of cancer cells. While membrane ty- rosine-kinase receptors are known to dimerize, Src is classified as a non-receptor kinase and assumed to remain always mono- meric. Here we demonstrate the formation of stable dimers by the first domains of myristoylated Src previously shown to be sufficient for Src trafficking. Src dimers fused to green fluo- rescent protein (GFP) on supported lipid bilayers were identi- fied using single-molecule photobleaching experiments. Com- petition with a protein containing only native Src domains without GFP confirms that dimerization is a previously over- looked intrinsic property of Src. Dimerization is concomitant to membrane binding by the myristoylated forms of Src and may constitute a new regulation layer for the Src oncogene.