Cajal-Retzius (CR) cells are a transient type of neurons that populate the postnatal hippocampus. The role of transient cell types and circuits have been vastly addressed in neocortical regions, but poorly studied in the hippocampus. To understand how CR cells persistence influences the maturation of hippocampal circuits, we specifically ablated CR cells from the postnatal hippocampus. Overall design: Our results highlighted a layer-specific effects on dendritic spines and synaptic-related genes and revealed a critical role of CR cells on the establishment of the hippocampal network.