Complete decompression is very important for the surgical treatment of the spinal stenosis. But it may produce the segmental instability or spondylolisthesis as postoperative complications. So rigid internal fixation is mandatory to reduce this problem. Authors treated 16 cases of spinal stenosis by complete decompression and pedicale screw fixation and posterolateral fusion, analyzed 11 cases which were followed more than 9 months. The results were as follows: 1. Among the 11 cases, the mean age was 49 years old and there were 5 males and 6 females. 2. The most common cause was degenerative type, 7 cases. The most frequent level of involvement was L4–L5, 10 cases and two level involvement was 3 cases. 3. Among the 11 cases, 6 cases were excellent and 4 cases were good, and 1 case was fair, in Hanley's criteria. 4. In spondylolisthetic stenosis, the average percentage of slippage was changed from 22% pre-operatively to 2.7% postoperatively and 3.8% after 9 months follow up. 5. The complications were relatively few(1 case of hematoma and 3 cases of pain on the bone graft donor site).