Abstract Synaptotagmin IV (Syt IV) is a secretory vesicle protein that is broadly expressed in brain and may function as a presynaptic regulator of synaptic release. Because Syt IV and abnormalities in neurotransmission have been implicated in psychiatric disease, we examined Syt IV (−/−) mice in animal models of mood-related behavior. We report that Syt IV (−/−) mice display lower levels of anxiety-like behavior in the elevated plus maze and enhanced locomotion in the open field. Syt IV (−/−) mice also exhibit reduced depression-like behavior and are highly sensitive to the effects of the anti-depressant imipramine in a modified Porsolt forced swim test. However, the physical restraint-induced stress hormone response is normal in Syt IV (−/−) mice. As judged by immunohistochemical criteria, the synaptic structure and connectivity of the hippocampus and raphe nucleus in Syt IV (−/−) mice are indistinguishable from wild-type littermates. These results indicate that Syt IV plays a role in rodent mood-related behavior and suggests Syt IV regulates synaptic function in the neuronal networks that modulate these behaviors.