Fine-tuning of synaptic connectivity during development is guided by intrinsic activity of the immature networks characteristically consisting of intermittent bursts of synchronous activity. However, the role of synchronous vs. asynchronous activity in synapse maturation in the brain is unclear. Here we have pharmacologically prevented generation of synchronous activity in the immature rat CA3-CA1 circuitry in a manner that preserves unitary activity. Long-term desynchronization of the network resulted in weakening of AMPA receptor-mediated glutamatergic transmission in CA1 pyramidal cells. This weakening was dependent on protein phosphatase and mGluR activity, associated with an increase in the proportion of silent synapses and a decrease in the protein levels of GluA4 suggesting postsynaptic mechanisms of expression. The findings demonstrate that synchronous activity in the immature CA3-CA1 circuitry is critical for the induction and maintenance of glutamatergic synapses and underscores the importance of temporal activity patterns in shaping the synaptic circuitry during development.