The study investigated the influence of lumbar flexibility exercise on the lumbar angle among patients with non-specific low back pain (LBP). Pre-experimental one-group pretest-posttest design trial was conducted at Health Service Center, Chulalongkorn University, Thailand. Thirty-five non-specific LBP patients with limitation in lower back range of motion and without neurological deficits were recruited (based on the LBP guidelines by RCGP 1999). Lumbar flexibility exercise program developed based on McKenzie therapy was performed individually each day for 2 weeks. Patients attended an exercise program daily in the first week under the supervision of a physiotherapist. The exercise program consisted of 7 sets a day (3-2-2 in the morning-afternoon-evening) in series of 10 repetitions for each set for 2 weeks. Lumbar angle was measured at the beginning and at the end of 2 weeks in order to determine the range of motion improved. The results indicated that the low back pain symptom improved as well as the angle.