Using Western blotting technique, the effects of auditory deprivation and tone exposure on the relative expression level (REL) of NMDA receptor subunit NR2B protein of rat auditory cortex during early postnatal days were studied. The results showed that the NR2B protein expression of PND14 and PND28 decreased significantly (P < 0.05, P < 0.01) when auditory deprivation for 7 days. Tone exposure after auditory deprivation for 7 days made NR2B protein level increased significantly (P < 0.05). It showed bidirectional regulation of NMDA receptor subunit NB2B protein. No significant effects of auditory deprivation and tone exposure on the relative expression level of NR2B protein of PND42 (P > 0.05) were found. The results indicated that, auditory deprivation and experience can modify the protein expression level of NMDA receptor subunit NR2B during the critical period of rat postnatal development. The findings provided important data to the study of the mechanisms for the developmental plasticity of sensory functions.