Using conventional electrophysiological technique, the plasticity of characteristic frequency (CF) of neurons in rat auditory cortex (AC) at postnatal age of two, three, four, five, six and eight week was investigated by determining CF and frequency tuning curve (FTC) shifts of neurons. It was found that when the frequency difference between conditioned stimulus frequency (CSF) and CF of neuron was in 1.0 kHz with conditioned stimulation, conditioned stimulus can induce CF shift toward higher frequency side (HFS), lower frequency side (LFS) and both sides (BLH) of neuron's FTC. The proportion of CF shift becomes lower and the proportion of non CF shift becomes higher with the increasing of the age. Neurons with bigger Q₁₀-dB value and symmetry index >0 of the FTC, increasing of the proportion of CF shift toward higher frequency side (HFS) of neuron's FTC is much higher. There is significant correlation between the time course and the age of rat, the older is the age, the longer is the shift time (P < 0.05) and the recovery time (P < 0.05) of neurons. The results suggest that plasticity of characteristic frequency in rat auditory cortical neurons is correlated with the postnatal age. The findings provided important data to the study of the mechanisms for the developmental plasticity of central nervous system.