Purpose: There is a lack of evidence about trunk muscle endurance, range of motion (ROM), flexibility and quality of life (QoL) in subjects with adolescent idiopathic scoliosis (AIS) following posterior instrumentation and fusion (PIF) surgery. The study aimed to compare trunk muscle endurance, ROM, flexibility, and QoL of the AIS subjects with lumbar or thoracic level after surgery. It also investigated the relationship between trunk muscle endurance, ROM, flexibility, and QoL in subjects with AIS. Methods: Twenty subjects aged between 10-18 years (mean age=15.55±1.46 years) who underwent PIF surgery before 1-3 years were included. The subjects were divided into two groups as a thoracic (n=10) and lumbar group (n=10) according to the PIF surgery level. The ROM was assessed using a universal goniometer, flexibility with sit and reach test and lateral bending, trunk extensor muscle endurance assessed with Biering-Sorensen test, trunk flexor muscle endurance with the Kraus-Weber test, and the QoL through the Scoliosis Research Society-22 revised (SRS-22r) scale. Results: There was significant difference between the two groups in lateral flexion ROM and lateral bending results (p<0.05). Thoracic group showed better results in the lateral flexion ROM and lateral bending test. Trunk flexor muscle endurance was found correlated with extension ROM (r=0.718, p=0.001), flexion ROM (r=0.414, p=0.007), right lateral flexion ROM (r=0.721, p=0.001), and left lateral flexion ROM (r=0.581, p=0.007). Trunk extensor muscle endurance was found correlated with right rotation ROM (r=0.511, p=0.021), left rotation ROM (r=0.410, p=0.073), SRS-22r total score (r=0.677, p=0.001) and SRS-22r pain score (r=0.554, p=0.011). Conclusion: Trunk muscle endurance is essential for body posture and QoL after surgery. These subject’s physiotherapy and rehabilitation programs should focus on developing trunk muscle endurance and flexibility to increase QoL following PIF surgery.