Dvl, an important component of the Wnt signalling pathway, is thought to be involved in synaptogenesis. In this study, we investigated whether Dvl regulates neurotransmitter release. Knockdown of Dvl in PC12 cells suppressed K(+)-induced dopamine release, and this phenotype was restored by expression of Dvl-1. We identified synaptotagmin (Syt) I, which is involved in neurotransmitter release, as a Dvl-binding protein. Dvl directly bound to the C2B domain of Syt I. Dvl colocalized with Syt I at the tip of neurites of differentiated PC12 cells and of neurons in the rat dorsal root ganglion. Dvl and Syt I was located in large dense-core vesicles, which contain dopamine. In addition, endocytosis of vesicles containing Syt I was suppressed in Dvl knockdown PC12 cells. Dvl inhibited the binding of Syt I to the complex consisting of syntaxin-1A and SNAP-25. Furthermore, micro2-adaptin of AP-2, which is known to play a role in endocytosis, formed a complex with Dvl and Syt I. Taken together, these results suggest that Dvl is involved in endo- and exocytotic processes through the binding to Syt I.