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This study demonstrates the monitoring of distributed strain of rail and girder of a railway bridge occurring during train passage over the bridge’s entire section on a real-time basis by applying a developed distributed optical fiber sensor based on Brillouin Optical Correlation Domain Analysis (BOCDA). The distributed optical fiber sensor system and an algorithm to control as well as to analyze Brillouin gain spectrum signals were also developed. A single-mode optical fiber was attached in the longitudinal direction on the rail and the lower flange of the girder to be used as a sensing fiber of the BOCDA system. Changes in the girder’s strain at the center point of the bridge during the passage of a commercial train were measured at 9 Hz, and the accuracy of this measurement was validated by comparing the measured data with the data from strain gauge. In addition, the distributed strain of a girder and the rail with a length of 40.26 m was measured in real time with a spatial resolution of 31.1 cm. Based on the results of the rail’s strain distribution, the study could identify the location where excessive strain occurred due to an influence of unsupported sleepers on girder of the bridge. [ABSTRACT FROM AUTHOR]