In this paper, the dynamic behavior of an existing long-span railway bridge in Afyon-Turkey, subjected to different earthquake ground motion is investigated. In this study a full two-dimensional finite element model of the railway bridge system was established, in which the soil-structure interactions were considered. Time domain dynamic analyses of the bridge-soil models and also a 2D version of PLAXIS, a specially developed finite element software for solving geotechnical problems, have been performed. Considering the soil property of railway bridge site, analysis was performed for one type of soil, which is specified as soft. Manjil (Iran, 1990), Kobe (Japan, 1995) and Kocaeli (Turkey, 1999) earthquakes are defined as input motions. According to the result of the dynamic analysis, the relative displacements in both directions (x and y) for the top point of bridge (Point A), base point of bridge (Point B) and soil levels (Point C, without bridge structure) were obtained and showed as graphic form. The displacement values are different for each kind of earthquake ground motions, hence it means that the bridge structure and soil have different responses to each kind of earthquake ground motions. Keywords: Railway Bridge, Seismic Behaviour, Soil-Structure Interaction, Finite Element Method (FEM), Soft Soil, Displacement, Plaxis 2D.