Detoxication effect of red ginseng on the fine structure of cerebellum in goldfish treated with endosulfan was investigated by means of electron microscopy. The brain neurons of endosulfan exposure group showed dilation of dendrites and axons, numerical decrease of ribosomes, and considerable swelling of mitochondria as compared with the normal neuron. There were slight swelling of mitochondria, some dilation of dendrites and axons, and numerical increase of ribosomes in the neuron of endosulfan-red ginseng treatment group as compared with the endosulfan exposure group. It might be concluded that red ginseng has detoxication effect on injured brain tissue induced by endosulfan toxicity.