Piccolo is one of the components of the active zone at chemical synapses and regulates the transport of synaptic vesicles. The piccolo C2A domain is an important calcium sensor and binds with phosphatidylinositol or synaptotagmin-1. Recently, clinical studies suggested that a single nucleotide polymorphism in the piccolo C2A domain might be a causal risk factor for major depression. To clarify the association of piccolo with depression, we produced a transgenic mouse overexpressing the C2A domain of piccolo, and investigated the behavior of these mice. The mice exhibited depression-like behavior in both forced swim and tail suspension tests, suggesting that piccolo might regulate the depressive behavior.