Background: Non-specific low back pain (NSLBP) in adolescence is common and crucial problem that affects a child's ability to function in daily life, their relationships with others, their happiness, and their mental health. Also, it may become compounded into adulthood. Williams and McKenzie exercises are the most commonly used to treat patient's back pain. Objective: This study aimed to compare between Mckenzie and William exercises regarding their affection pain, spinal flexibility and balance for adolescents with NSLBP. Patients and methods: A total of 34 adolescent males with NSLBP participated in this study. Those who met the criteria for inclusion, were divided randomly into two groups; Group A received Mckenzie extension exercises; and Group B received William flexion exercises. Data was collected from groups pre-treatment, 2 and 4 weeks post-treatment (Post I and II) regarding visual analogue scale, flexibility score, vestibular balance and balance board scores. Results: Comparative analysis showed that both groups were similar at baselines. Patients in both study groups showed significant reduction of pain and improvement in spinal flexibility and balance. No significant differences were observed between the effectiveness of McKenzie and William exercises on pain, flexibility and balance for treating NSLBP in adolescents. Conclusions: Both McKenzie extension exercises and William flexion exercises are effective in treating adolescents with NSLBP. The effectiveness of both exercises regarding pain, spinal flexibility and balance were comparable.