Background: Low Back Pain (LBP) is the mosthighly prevalent musculoskeletal disorder. Now, it can be considered the most common cause of disability in the world. Strongconnections have been reported between low back pain prevalence and disturbance of back muscle flexion relaxation phenomenon (FRP). Aim of Study:To determine the effect of lumbar posture on back muscles flexion relaxation phenomenon during sitting in chronic non-specific low back pain (CNSLBP) among faculty of physical therapy students. Conclusion:Lumbar posture has asignificant effect on erector spinae activation and consequently the flexionrelaxation phenomenon among students withchronic nonspecific low back pain.