Msny clinical and experimental studies trying to elucidate the cause of idiopathic scoliosis have been carried out. There, however, is no established theory to explain it. This paper is aimed at approaching one of various causes of idiopathic scoliosis by producing thoracic scoliosis in growing rabbits with unilateral resection of thoracic spinal nerves. All 43 rabbits were divided into four different groups. The first group(11 rabbits) consisted of rsbbits whose primary anterior and posterior divisions of the unilateral thoracic spinal nerves were resected. The second(11 rabbits) and the third(11 rabbits) were groups of rabbits whose primary anterior and posterior devisions were resected respectively. The fourth(10 rabbits) was the control group. The first group of rsbbits showed the most prominent curvature of the spine. The group of resection of primary posterior division showed less severe scoliosis than the first group but more marked scoliosis than the group of resection of primary anterior division. The biopsy of the denervated muscles included in the scoliosis revealed atrophy. It is concluded from the animal experiments with 43 growing rabbits that unilateral paralysis of the thoracic spinal nerves could be one csuse of iniopathic scoliosis and the primary posterior division of the thoracic spinal nerve contributed to the production of scoliosis more than the primary anterior division.