The biomechanical stability of the lumbar spine after two surgical procedures of total facetectomy and osteoplastic laminectomy was investigated using fresh-frozen human cadaveric lumbar spine specimens. Six pure moments in flexion-extension, right-left bending, and right-left twisting were applied and intervertebral motions were recorded using an optoelectronic motion measurement system. Neutral zone (NZ) and range of motion (ROM) under three conditions of intact, total facetectomy, and osteoplastic laminectomy were analyzed statistically to determine comparative biomechanical potential for instability. Results of NZ showed no changes in any direction with respect to the intact behavior after the two procedures. Also, in lateral bending, there were no significant increases in ROM after the two procedures. However, flexion-extension ROM increased significantly (+33%, p < 0.05) after the total facetectomy, but not after osteoplastic laminectomy. Axial rotation ROM increased remarkably after the total facetectomy (+113%, p < 0.05), but only moderately (+57%, p < 0.05) after the osteoplastic laminectomy. The osteoplastic laminectomy, which preserves the spinous process as well as the facet joints, maintains greater spinal stability than the total facetectomy.