Introduction: We previously reported sex differences in the developmental trajectories of contextual learning function and found multiple critical periods for hippocampal function in male rats. Here, we focus on training-induced hippocampal CA1 synaptic plasticity in early childhood to analyze sex differences. Methods: Male (n = 27) and female (n = 18) rats at 16-17 days of postnatal age were subjected to a hippocampal-dependent inhibitory avoidance (IA) task. CA1 neurons received inputs from CA3 and the entorhinal cortex (EC) via different synaptic pathways. Brain slices were then analyzed to assess CA1 synaptic plasticity, focusing on changes in the ratio of AMPA receptor- / NMDA receptor-mediated postsynaptic currents, and single-vesicle-induced miniature excitatory and inhibitory postsynaptic currents (mEPSCs and mIPSCs). Behavioral battery tests evaluated sensory, motor, and emotional functions. Results: IA learning was established in females (P < 0.01) but not in males, indicating sex differences in contextual learning ability without changes in basic sensory/motor functions. In the emotional state, females showed more sociability with others than males (P < 0.05). Frequency of mEPSCs and mIPSCs decreased in males after learning (P < 0.01), whereas mIPSCs frequency increased in females (P < 0.05). Furthermore, AMPA/NMDA ratios increased in the CA3-CA1 and ECIII-CA1 pathways after learning, suggesting a predominance of AMPA receptor-mediated synaptic plasticity after learning (P < 0.01). Unpaired t-tests were used to analyze the results. Conclusion: Female infants showed faster development of hippocampal learning and induced plasticity than male infants, indicating a clear sex difference. These findings provide synaptic evidence for sex-specific development of contextual learning and training-induced plasticity at CA1 synapses.