Proteins from the NANOS family are conserved translational repressors with a well-known role in gonad development in both vertebrates and invertebrates. In addition, Drosophila Nanos controls neuron maturation and function, and rodent Nanos1 affects cortical neuron differentiation. Here we show that rat Nanos1 is expressed in hippocampal neurons and that the siRNA-mediated knockdown of Nanos1 impairs synaptogenesis. We found that both dendritic spine size and number were affected by Nanos1 KD. Dendritic spines were smaller and more numerous. Moreover, whereas in control neurons most dendritic PSD95 clusters contact pre-synaptic structures, a larger proportion of PSD95 clusters lacked a synapsin counterpart upon Nanos1 loss-of-function. Finally, Nanos1 KD impaired the induction of ARC typically triggered by neuron depolarization. These results expand our knowledge on the role of NANOS1 in CNS development and suggest that RNA regulation by NANOS1 governs hippocampal synaptogenesis.