Degenerative lumbar disc conditions are the main cause to nerve roots compression. Lumbar spine decompression and fusion have been considered the gold standard operation in managing lumbar degenerative disc disease after failure of conservative measures. Purpose: To compare bone fusion rate using flexible and rigid rods with posterolateral fusion in patients with degenerative lumbar disc diseases. Patient sample: Prospective study of 50 patients with degenerative lumbar disc disease. Twenty-five patients were treated by lumbar posterolateral fusion using flexible rods (group 1) while the other twenty-five patients were treated by rigid rods (group 2). Outcome measures: functional evaluation by fusion rate was detected in the first group fused with flexible rods, compared to the second group fused with rigid rods. Methods: This study was conducted in the spine unit at Cairo university hospital, Shark El-Madinah Hospital, Alexandria, Egypt on 50 patients with degenerative lumbar disc disease. Twenty-five patients were treated by lumbar posterolateral fusion using flexible rods (group 1) while the other twenty-five patients were treated by rigid rods (group 2). Results: Fusion rate was faster in the first group fused with flexible rods, compared to the second group fused with rigid rods. Conclusion: When performing posterolateral fusion with flexible titanium rods in the treatment of degenerative lumbar diseases, the fusion rate was quicker than rigid rods. However, there was no clinical or radiological difference between the two fusion methods