Abstract Objective The present study is to evaluate the clinical outcomes of the sequential correction of severe and rigid kyphoscoliosis. Methods Between January 2014 and December 2020, 27 adults with severe and rigid kyphoscoliosis underwent sequential correction combined with posterior grade 4 or grade 5 spinal osteotomy. Radiological parameters, including the major curve Cobb angle, kyphotic angle, coronal imbalance, and sagittal vertical axis (SVA), were compared. Patient self-reported health-related quality of life (HRQOL) scores were used to evaluate clinical outcomes. Results The mean major curve Cobb angle improved from 134.30 ± 13.24° to 44.48 ± 9.34° immediately after surgery and to 46.11 ± 8.94° at the final follow-up. The mean kyphotic angle improved from 112.15 ± 20.28° to 38.63 ± 15.00° immediately after surgery and to 39.85 ± 14.92° at the final follow-up. The mean preoperative major curve Cobb angle of grade 5 spinal osteotomy group was higher than that of grade 4 spinal osteotomy group. Coronal imbalance and SVA slightly improved. The patient self-reported HRQOL scores improved postoperatively and at the final follow-up. Activity, appearance and total scores of the SRS-22 of the grade 5 spinal osteotomy group at the final follow-up were significantly better than those of the grade 4 spinal osteotomy group. Conclusions Sequential correction combined with posterior grade 4 or grade 5 spinal osteotomies is an excellent and safe treatment for severe and rigid kyphoscoliosis in adults. Sequential correction combined with posterior grade 5 spinal osteotomies can be used to correct severe and rigid kyphoscoliosis with higher major curve Cobb angle.