Capsaicin, the pungent algesic substance of red pepper, has various effects on the cardiovascular system, respiratory system, digestive system and nervous system. To investigate the capsaicin effects on the enteric nervous system, capsaicin was administered to the neonatal and the adult rats and morphometric and electron microscopical studies have been done. Capsaicin (50mg/kg) was injected subcutaneously in the 2nd and 4th day after birth and to the adult rats, same amount was injected once subcutaneously. Experiment was performed 5, 10, 20, 30 days and 10 weeks after injection in the neonatal rats and 1 week after injection in the adult rats. NADH-TR stain was performed in whole mount preparation of small intestine and the number of neurons in the myenteric plexus and in one enteric ganglion was counted and size of the enteric neurons was measured. The ultrastructural changes were observed by electron microscopy. The results obtained were as follows : The number of enteric neurons in unit area (5487μm2) decreased significantly in the experimental group and this phenomenon was prominent in the ileum. The number of enteric neurons per one ganglion decreased also significantly in the experimental group and this was also most prominent in the ileum. The cell area of the enteric neurons increased as the animals grow and increment was most prominent in 20 days after birth. Size decrement was observed generally in the experimental group. In electronmicroscopical finding, cell organelles changes were observed from experimental 10 day group and cell degeneration was prominent in 20 day group and these were continued to 10 week group.