Although several kinds of instrumentation systems are available for the transpedicular screw fixation in the treatment of spondylolisthesis, the clinical results and the difference between them remdins unclear. In order to study the feasibility of Zielke instrumentation system for that purpose, the author analysed the clinical results of 73 patients with mild or moderate degree of spondylolisthesis who were instrumented with the systems and followed up 25 months in average(Min. 12Ms). The results between the groups with different rod thickness in the system, 3.2mm(20 pa - tients), 4mm(33 patients) and 5mm(20 patients), were compared to study the most appropriate thickness. Reduction of the deformity were done by aid of temporarilly applied Harrington system in 3.2mm group. Inlayed reduction potential coming from the jointing mechanism was utilized in the cases with less than 30% of slippage in 4 and 5mm group. Percentage of slippage was changed from 20% preoperatively, to 4% postoperatively and 6% at the end of follow up. The methods of fusion after reduction and fixation were anterior in 25 and posterolateral in 48. Bony fusion was achieved in all but one with pathological spondylolisthesis. Rod failures were observed in two of 3.2mm and one of 4mm group, and loosening of the joint were developed in three of 5mm group. Clinically, 93% of the patient showed excellent and good results at the end of follow up. From the results, we concluded that the instrumentation is a efficient method of treatment with several advantages in the reduction capacity and the stability of fixation. However, this system has several points in its mechanics that needs to be improved.