Objective To investigate the effect of asymmetric lumbar discectomy on facet joint force and stability of lumbar spine. Methods Seven human cadaver specimens (L2-3 segment) were selected to make intact, 1/4 discectomy and 1/2 discectomy status and applied with pure moment of 7.5 N?m. The range of motion (ROM) and facet joint force of L2-3 segment during flexion/extension, lateral bending and axial rotation were recorded, respectively. Results During extension, a significant increase in facet joint force was found under 1/4 discectomy status at the remained side. During lateral bending, the facet joint force at both sides under 1/2 discectomy status increased significantly than that under intact status. During axial rotation, facet joint force increased significantly only at the side without discectomy under 1/2 discectomy status. Except flexion, ROM under 1/4 discectomy and 1/2 discectomy status were larger than that under intact status in all the other motion directions (P<0.05). There was no significant difference in ROM between both sides during lateral bending and axial rotation direction. Conclusions The asymmetric lumbar discectomy can increase the ROM in all motion directions except flexion, and can enlarge the facet joint force asymmetrically, which indicate that instability of lumbar spine and facet joint force increasing resulted from asymmetric degeneration of the disc might lead to backache.