Syndecan‐4, a member of the syndecan gene family of proteoglycans, is an important regulator of bFGF signaling. In particular, bFGF‐dependent regulation of cell growth and migration has been linked to syndecan‐4 cytoplasmic domain‐mediated interactions. Screening of a yeast two‐hybrid library with a cytoplasmic domain of rat syndecan‐4 identified a novel binding partner, here termed synectin. Synectin is highly homologous to semaphorin F binding protein semcap1, glucose 1 transporter binding protein glut1cbp, and RGS‐GAIP/neuropilin‐1 binding protein GIPC. Overexpression of synectin in ECV304 cells in culture led to a dose‐dependent inhibition of migration while not affecting cell adhesion or growth rate. We conclude that synectin is involved in syndecan‐4–dependent interactions and may play a role in the assembly of syndecan‐4 signaling complex. J. Cell. Physiol. 184:373–379, 2000. © 2000 Wiley‐Liss, Inc.