Sacroiliac joint dysfunction is a term often used to describe pain in and around the region of the joint that is presumed to be due to biomechanical disorders of the joint. Despite of high incidence, the contribution of sacroiliac joint to low back pain has been a matter of controversy. Physical therapists routinely assess spinal range of motion in patients with low back pain and believe that spinal range of motion and disability are closely linked. The present study was aimed to determine the relative efficacy of Muscle Energy Technique as compared to Conventional Therapy on lumbar spine range of motion in chronic low back pain of Sacroiliac origin. It was found that the subjects who were treated with Muscle Energy Technique showed greater improvements in lumbar spine range of motion as compared to Conventional Therapy Group. As far as reduction in pain and disability are concerned both the groups showed almost similar results. The study concluded that sacroiliac joint dysfunction affects lumbar spine range of motion and is a significant contributor to chronic low back pain.