The Purpose of this study was to investigate the change of lumbar extensor strength according to lumbosacral angle on chronic lumbar back pain patients. For this investigation lumbar extensor strength was administered to 60 patients who were diagnosed chronic lumbar back pain The subjects was to investigate lumbosacral angle in standing position and it were calculated lumbar extensor strength by using Medex. The result of this study summarized are as follows ; 1. Total experimental group exhibited significantly higher difference than control group in lumbar extensor strength among all degree lumbosacral angle. 2. In the relationship between experimental group and control group in lumbar extensor strength among lumbosacral angle, all degree difference was revealed II, I, III order. 3. In the relationship between experimental group and control group in lumbar extensor strength among lumbosacral angle, I group difference was did not. 4. In the relationship between experimental group and control group in lumbar extensor strength among lumbosacral angle, all degree among II group was noted significantly difference except 24, 72 angle. 5. In the relationship between experimental group and control group in lumbar extensor strength among lumbosacral angle, control group was revealed higher muscle strength 48, 60, 72 angle, however no significantly difference was noted 0, 12, 24 angle. The study was objected difference of other group in both of experimental and control group. Because lumbar extensor weakness with bad position was gradually increased back pain, to Maintain normal lumbosacral angle befor exercising lumbar extensor strength was most important.