Lumbar spinal flexion and extension motion was measured radiographically- "invasive" and from the back surface curvature- "non-invasive" (using motion analysis system)for evaluating lumbar spinal mobility(LSM). Twenty-four volunteers participated in this study and had their lateral view of lumbar spinal radiographs and photographs taken in three postures(upright, flexion and extension). The lumbar sacral angles(LSA) and the angles of each vertebral segment were obtained both from skin surface curvature and picture of X-ray. The results showed that the LSA and LSM remained the same either calculated based on Cobb angle or overly angle definition. To transform skin marker coordinates into corresponding vertebral body coordinates, a third order regression model was developed.The proposed transformation model demonstrated high coefficient of determination (mean=84.05%)between transformed positions and actual positions in all vertebral bodies, Based on this model, global LSA and intersegmental spinal mobility were recalculated and compared with results from X-ray measurement data. The results showed that the inter-vertebral lumbar spinal mobility could be obtained with errors ranging from 0.06 to 0.62 degrees. The results of this study indicated that in addition to the total motion in region of lumbar spine, we are able to discriminate the contribution of intersegmental spinal mobility through way of "non-invasive" measurement.