Auditory function can be affected by many factors, including environment and experience. In this study, we investigated whether early auditory experience mediates the regulation of the composition/ratio changes of the N-methyl-D-aspartic acid (NMDA) receptor subunits during development of the rat auditory cortex. We found that early sound exposure can increase expression of the NMDA receptor subunits and increase the composition/ratios of NMDA receptor subunits during the postnatal critical period. D-2-amino-5-phosphonovaleric acid (D-APV) could block and reverse the auditory experience-mediated changes, and there were marked reductions in expression levels and the composition/ratios of NMDA receptor subunits. These results indicate that the experience-dependent plasticity of the auditory cortex in the critical period during postnatal development has a marked influence on NMDA receptor expression in the rat and that changes in NMDA receptor subunit composition/ratios might mediate the early auditory experience-dependent plasticity crucial to auditory function. © 2008 Wiley-Liss, Inc.