To study the variation of nitric oxide synthase (NOS) neurons in rats with learning-remembering barrier by immunohistochemistry and histochemistry. The number of NOS neurons decreased apparently in hippocampus CA1-4 of rats with learning-remembering barrier, there were lots of new NOS neurons in dentate gyrus granular cell grays and pear-shaped zone's cortex. It is suggested that NOS neurons of hippocampus exert very important action in rat's learning remembering; new NOS neurons in pear-shaped zone cortex and dentate gyrus granular cell grays may be a compensative reaction of the learning-remembering barrier, and they might exert important function in following recovery of learning-remembering function.