The segmental and regional projections of the sciatic, tibial and common peroneal nerves to the substantia gelatinosa of spinal cord in rats were studied with the acid phosphatase method. Experiments were carried on 42 rats. Under chloral hydrate anesthesia, sciatic, tibial and common peroneal nerves were severed respecively. Then, after a survival time of 5～12 days, the lumbosacral segments of the spinal cord were removed and sectioned. The frozen sections were incubated with the modified Gomori's method.The projections of the sciatic and tibial nerves to the substantia gelatinosa (SG)were found in L_2～S_1, while these of the common peroneal nerve in L_(2～6).The projections of the sciatic nerve were found in the most medial, the intermediate and the most lateral parts of SG in the segments L_(2～3), and in entire SG in the segments L_4～S_1.The projections of the tibial nerve were shown in the most medial and the intermediate parts of SG in the segments L_(2～5), and in the medial parts of SG at L_6～S_1.The projections of the common peroneal nerve were found in the intermediate parts of SG in all segments L_(2～6).The above study has provided anatomical data for probing into the mechanism of somatosplanchnic interrelations and the principle governing acupuncture anesthesia.