The results revealed that the number of cells significantly decreased at the ages of 25 and 28 months, with degeneration and atrophy of some cells, destruction of Nissi granules and myelin sheath with neurofilamentous accumulation. These changes were minimal at the age of 15 months aged rats. These results indicated that the senility which started at the age of 25 months has adverse effects on the auditory cortex of the rat.