The mechanical properties of materials for spinal fixation can significantly affect spinal surgical outcomes. Traditional materials such as titanium exhibit high stiffness, which can lead to stress shielding and adjacent segment degeneration. This study investigates the biomechanical performance of titanium and PEEK (polyetheretherketone) in spinal fixation using finite element analysis, through the evaluation of the (). A three-dimensional finite element analysis (FEA) model of an L4/L5 functional spinal unit was developed to simulate the mechanical behavior of three fixation systems: titanium screws and rods (model A), titanium screws with PEEK rods (model B), and PEEK screws and rods (model C). The analysis evaluated stress distribution and load transfer under physiological conditions, in comparison with the intact spine (baseline model). : The analysis showed that titanium fixation systems resulted in higher stress shielding effects, with a significant difference in stress distribution compared to PEEK. The maximum stress recorded in the neutral position was 24.145 MPa for PEEK, indicating better biomechanical compatibility. : The results suggest that PEEK may be an attractive alternative to titanium for spinal fixation, promoting more healthy load transfer and minimizing the risk of stress shielding complications.