The aim of this paper is to determine the earthquake behaviour of the Kömürhan Highway Bridge, located at the 51st kilometre of the Elazığ-Malatya highway over the Fırat River, after finite element model updating using operational modal analyses. Finite element models of the bridge are built with the SAP2000 program to obtain analytical dynamic characteristics such as natural frequencies and mode shapes. The ambient vibration tests are performed using operational modal analysis under traffic loads to attain experimental dynamic characteristics. Vibration data is gathered from both the box girder and bridge deck to compare the results. Measurement time, frequency span, and effective mode number are determined following similar studies and literature. The peak picking method in the frequency domain is used for output-only modal identification. The finite element model of the bridge is updated by changing some uncertainties in the parameters such as material properties and boundary conditions to eliminate the differences between analytical and experimental dynamic characteristics. An analytical model of the bridge after finite element model updating is analyzed using the 1992 Erzincan, Turkey earthquake record, which occurred near the region, to determine the earthquake behaviour of the bridge. At the end of the study, the maximum differences in the natural frequencies are reduced on average from 10 % to 2 %, and a good agreement is found between analytical and experimental natural frequencies and mode shapes by model updating. Also, the variation of internal forces such as bending moment, axial forces, and shear forces for the bridge deck and columns are presented in detail.