Objective To define the criteria of posterior selective thoracic fusion in patients with adolescent idiopathic scoliosis.Methods By reviewing the medical records and roentgenograms of 17 patients with adolescent idiopathic scoliosis who underwent posterior selective thoracic fusion, the curve type, Cobb angle, apical vertebral rotation and translation, trunk shift, and thoracolumbar kyphosis were measured and analyzed.Results There were 17 King type Ⅱ patients (PUMC type: Ⅱb1 13, Ⅱc3 4). The coronal Cobb angle of thoracic curve before and after operation were 56.9°and 21.6° respectively, the mean correction rate was 60.1%. The coronal Cobb angle of lumbar curve before and after operation were 34.8° and 12.1° respectively, and the mean spontaneous correction rate was 64.8%.At final follow-up, the coronal Cobb angle of thoracic and lumbar curve were 23.5° and 15.2° respectively, there were no significant changes in the coronal Cobb angle, apical vertebral translation and rotation compared with that after operation.One patient had 12° of thoracolumbar kyphosis after operation, no progression was noted at final follow-up. There was no trunk decompensation or deterioration of the lumbar curve. In this group, 3.9 levels were saved compared with fusing both the thoracic and lumbar curves.Conclusion Posterior selective thoracic fusion can be safely and effectively performed in King type Ⅱ patients with a moderate and flexible lumbar curve, which can save more mobile segments and at the same time can maintain a good coronal and sagittal balance.