The present study examined the impacts of the mechanical properties of the filling material on the seismic behaviour of masonry arch bridges (MAB). A bridge model that did not exist was selected to achieve this objective. Using this model, bridge models with different filling material properties were created in the SAP2000 computer program. Modal analysis and linear time history analysis (THA) were conducted on the aforementioned models to ascertain the filling material's influence on the bridge's dynamic behavior. The findings of the modal analysis indicated that an increase in the density of the filling material increased in the period, while an increase in the elasticity modulus led to a decrease in the period. As a result of linear THA, it was determined that as the density of the filling material increases, the displacements and stresses increase, and as the elastic modulus increases, the displacements and stresses decrease. As a result of static analysis, it was determined that as the density of the filling material increases, the displacement and stress values increase, and as the elastic modulus increases, these values decrease.