Purpose <p>Prestressed concrete (PSC) box girder bridges offer superior strength compared to reinforced concrete box girder bridges and provide larger spans than reinforced concrete bridges. PSC box girder bridges have become more common due to their numerous structural and architectural advantages. The PSC bridge is one of the structures with multiple masses that allows each mass to take part in the free vibration response. Earlier researchers did not examine the influences of prestressing on the modal performance of a bridge. This modal investigation aims to find the natural frequency and mode form for the PSC box girder bridge with and without considering the effect of prestressing force.</p> Methods <p>The modal evaluation of the PSC box girder bridge uses the Finite Element Method (FEM) software model.</p> Results and Conclusion <p>The study’s significant findings are the determination of the natural frequency and mode shape of the bridge, considering and not considering the effect of prestressing force. The natural frequencies of the bridge are increasing due to the effect of the prestressing force. The present inquiry is confined to the modal performance of the system. This investigation may serve as a framework for the next phase of analysis of the dynamics of box-girder bridges subjected to fluctuating vehicle loads.</p>