Using post tensioned cables becomes one of the most effective methods in strengthening different types of structures especially steel structure. This paper studies the effect of post tensioned cables in strengthening double span steel trusses. Different truss’s systems (Warren and N truss system) are included in this study. Different techniques using post tensioned cables are used in strengthening different truss’s systems. The main difference between these techniques is the profile and the locations of the post tensioned cables. Comparisons between these techniques are made in order to determine the suitable post tensioning technique for each truss system. The analysis and results are obtained by using ANSYS program.