Objective To study the development and changes of the Barrel Cortex in younger and adult SD rats. Methods Cytochrome oxydase histochemistry and Nissl’s counterstaining were applied to locate the encephalic region of Barrel in adult rats, and Barrel cortex changes in different ages were analyzed(postnatal 20 days and postnatal 3 months). Results During the development of Barrel cortex, an obvious area change was found（EM>P/EM><0.01）. The space between Barrel rows shrinked and the number of neurons in septa decreased. Compared with that of younger Sprague-Dawley rats, the Barrel cortex of adult Sprague-Dawley rats had more cytochrome oxydase highly active neurons（EM>P/EM><0.01）.Conclusion Subtle changes exist during the development in the fine assignment and structure o