The purpose of this study were to compare the differences of isometric lumber extension strength and subjective pain degrees between obesity patients group and normal body fat group in disc surgical operated patients. The research purposed to indicate how isometric lumbar extension exercise for 12 weeks affected to lumbar strength and visual analogue scale of patients suffered by chronic back pain. The subjects were 65 low back pain patients(male 30, female 35)who had disease on lumbar in W hospital. The lumbar extension strength was measured at seven degrees of angles, which were $0^{circ}$ $12^{circ}$ $24^{circ}$ $36^{circ}$ $48^{circ}$ $60^{circ}$ and $72^{circ}$ before and after the exercise program. We got the results of subjective pain degree using the modified visual analogue scale(VAS) of Lawlis et al(1989) and measured the maximal isometric lumbar strength of all subjects using MedX lumbar extension machine. Results were as follows; After the exercise, the lumbar extension strength of normal body fat patients groups included males and female were greater than that of the obesity patients groups in all angles(p<.05). The visual analogue scale of chronic back pain patients was decreased significantly after the exercise(p<.05). The results showed the significance between the lumbar extension strength and the visual analogue scale of chronic back pain patients and showed that the isometric lumbar extension exercise decreased the subjective pain degrees of visual analogue scale with and increased lumbar extension strength. The correlation between the visual analogue scale and the %body fat of chronic back pain patients was no significant after exercise. Therefore, the lumbar extension strength exercise is needed for improvement of back strength, decrease of %body fat.