BACKGROUND: Early-onset scoliosis, which develops before 2 years of age and progresses rapidly, has been reported as an inevitable complication in spinal muscular atrophy (SMA) patients with 2 copies of the survival motor neuron 2 (SMN2) gene that receive post-onset disease-modifying therapy (DMT) within 6 months after birth. We describe a case of SMA type 0 in a patient with 2 copies of SMN2 that was treated with nusinersen, in which the patient's motor function improved and no progression of spinal deformity was observed. CASE PRESENTATION: The patient was born after an unremarkable gestation, but presented with severe muscle weakness immediately after birth. A genetic analysis conducted at 9 weeks of age revealed homozygous deletion of SMN1 and 2 copies of SMN2. He was diagnosed with SMA type 0 and treated with nusinersen from the age of 10 weeks. However, he required a tracheostomy and ventilatory management due to pharyngomalacia at 4 months. Slight spinal deformity was observed after sitting training was initiated at 1 year and 3 months. Physical therapy with careful postural management using a seating system and a supine stander was conducted twice a week to promote motor development. He was restricted to sitting without support for 30 min a day. At age 6, he can stand with support for several minutes, and scoliosis has been prevented. CONCLUSION: Our case suggests that early proactive, non-surgical management with targeted rehabilitation can prevent scoliosis progression in SMA patients with 2 copies of SMN2 that receive post-onset DMT within 6 months of birth.