Synapsin II (Syn II), a pivotal member of the synapsin family, is a synaptic vesicle-associated phosphoprotein which plays critical roles in regulating neurotransmitter release at both excitatory and inhibitory synapses within the central nervous system. Synapsins contribute significantly to synaptic plasticity and maintain the delicate balance between excitatory and inhibitory synaptic transmission. Notably, mutations in synapsins genes have been identified in forms of epilepsy with or without ASD. Syn II has been shown to interact with the presynaptic calcium channel P/Q, but the functional consequences of this interaction need to be studied. This study investigates the effects of SynII silencing by RNA interference in primary hippocampal neurons, focusing on its impact on excitatory transmission, intrinsic excitability and calcium current density. Our findings reveal that the knockdown of Syn II leads to increased spontaneous and evoked excitatory transmission associated with an increase in the calcium current density of P/Q-type channels. Additionally, Syn II silencing results in decreased excitability at the single-neuron level, but increased overall excitability at the network level. Collectively, these findings shed light on the complex role of Syn II in synaptic function and its ensuing impact on neuronal excitability due to the functional interactions with the P/Q-type calcium channel. This study provides a foundational understanding for future research in this domain, offering potential insights into the mechanisms underlying neuronal function.